U.S. Deputy Secretary of State, Wendy Sherman and South Korean Foreign Minister Chung Eui-yong talk prior to their meeting at the foreign ministry in Seoul, South Korea, July 22, 2021. Sherman is visiting South Korea to discuss North Korea's nuclear program and other regional and global issues. Song Kyung-seok/Pool via REUTERS

U.S. Deputy Secretary of State, Wendy Sherman and South Korean Foreign Minister Chung Eui-yong elbow bump prior to their meeting at the foreign ministry in Seoul, South Korea, July 22, 2021. Sherman is visiting South Korea to discuss North Korea's nuclear program and other regional and global issues. Song Kyung-seok/Pool via REUTERS

South Korean fishing boats take part in a marine protest, part of nationwide protests to demand Japan withdraw its decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, at the sea off Incheon, South Korea, April 30, 2021. The banners read "Condemning Japan's decision to release Fukushima water into the sea". REUTERS/Kim Hong-Ji

Members of the media take photographs of South Korean fishing boats taking part in a marine protest, part of nationwide protests to demand Japan to withdraw its decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, at the sea off Incheon, South Korea, April 30, 2021. The banners on the boats read "Condemning Japan's decision to release Fukushima water into the sea". REUTERS/Kim Hong-Ji TPX IMAGES OF THE DAY

A South Korean fisherman sits on his boat during a marine protest, part of nationwide protests to demand Japan withdraw its decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, at the sea off Incheon, South Korea, April 30, 2021. The banners read "Condemning Japan's decision to release Fukushima water into the sea". REUTERS/Kim Hong-Ji

A policeman films South Korean fishing boats taking part in a marine protest, part of nationwide protests to demand Japan withdraw its decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, at the sea off Incheon, South Korea, April 30, 2021. REUTERS/Kim Hong-Ji

South Korean fishing boats take part in a marine protest, part of nationwide protests to demand Japan withdraws its decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, at the sea off Incheon, South Korea, April 30, 2021. The banners on the boats read "Condemning Japan's decision to release Fukushima water into the sea". REUTERS/Kim Hong-Ji

A South Korean fisherman sits on his boat during a marine protest, part of nationwide protests to demand Japan withdraw its decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, at the sea off Incheon, South Korea, April 30, 2021. REUTERS/Kim Hong-Ji

A South Korea university student who got her head shaved, protests against Japan?s decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, in front of policemen protecting the Japanese embassy, in Seoul, South Korea, April 20, 2021. REUTERS/Kim Hong-ji

South Korea university students gets their heads shaved during a protest against Japan?s decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, in front of the Japanese embassy, in Seoul, South Korea, April 20, 2021. REUTERS/Kim Hong-ji

Shaved hairs of South Korea university students are seen during a protest against Japan?s decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, in front of the Japanese embassy, in Seoul, South Korea, April 20, 2021. REUTERS/Kim Hong-ji

South Korea university students gets their heads shaved during a protest against Japan?s decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, in front of the Japanese embassy, in Seoul, South Korea, April 20, 2021. Placard reads "Condemn Japan's decision to release contaminated water from Fukushima" REUTERS/Kim Hong-ji

A South Korea university student gets her head shaved during a protest against Japan?s decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, in front of the Japanese embassy, in Seoul, South Korea, April 20, 2021. REUTERS/Kim Hong-ji TPX IMAGES OF THE DAY

A South Korea university student gets her head shaved during a protest against Japan?s decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, in front of the Japanese embassy, in Seoul, South Korea, April 20, 2021. REUTERS/Kim Hong-ji

A South Korea university student gets her head shaved during a protest against Japan’s decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, in front of the Japanese embassy, in Seoul, South Korea, April 20, 2021. REUTERS/Kim Hong-ji

A South Korea university student gets her head shaved during a protest against Japan?s decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, in front of the Japanese embassy, in Seoul, South Korea, April 20, 2021. REUTERS/Kim Hong-ji

A South Korea university student gets her head shaved during a protest against Japan’s decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, in front of the Japanese embassy, in Seoul, South Korea, April 20, 2021. REUTERS/Kim Hong-ji

A South Korea university student gets her head shaved during a protest against Japan’s decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, in front of the Japanese embassy, in Seoul, South Korea, April 20, 2021. REUTERS/Kim Hong-ji

South Korea university students gets their heads shaved during a protest against Japan?s decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, in front of the Japanese embassy, in Seoul, South Korea, April 20, 2021. REUTERS/Kim Hong-ji

South Korea university students gets their heads shaved during a protest against Japan?s decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, in front of the Japanese embassy, in Seoul, South Korea, April 20, 2021. REUTERS/Kim Hong-ji TPX IMAGES OF THE DAY

South Korea university students gets their heads shaved during a protest against Japan’s decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, in front of the Japanese embassy, in Seoul, South Korea, April 20, 2021. REUTERS/Kim Hong-ji

A South Korea university student gets her head shaved during a protest against Japan?s decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, in front of the Japanese embassy, in Seoul, South Korea, April 20, 2021. REUTERS/Kim Hong-ji

A South Korea university student gets her head shaved during a protest against Japan?s decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, in front of the Japanese embassy, in Seoul, South Korea, April 20, 2021. REUTERS/Kim Hong-ji

A South Korea university student gets her head shaved during a protest against Japan?s decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, in front of the Japanese embassy, in Seoul, South Korea, April 20, 2021. REUTERS/Kim Hong-ji

A South Korea university student gets her head shaved during a protest against Japan?s decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, in front of the Japanese embassy, in Seoul, South Korea, April 20, 2021. REUTERS/Kim Hong-ji

A South Korea university student gets her head shaved during a protest against Japan?s decision to release contaminated water from its crippled Fukushima nuclear plant into the sea, in front of the Japanese embassy, in Seoul, South Korea, April 20, 2021. REUTERS/Kim Hong-ji

The facility is suspected of being a covert part of North Korea's nuclear weapons programme, possibly for enriching uranium fuel for weapons or producing components such as centrifuges.

North Korea's leader Kim Jong Un sits in his vehicle after arriving at a railway station in Dong Dang, Vietnam, at the border with China, February 26, 2019. Reuters Photographer Athit Perawongmetha: "I was assigned to cover Kim Jong Un's arrival by train in Dong Dang Ð the border town between Vietnam and China. I covered the North Korean leaderÕs first nuclear summit with U.S. President Donald Trump in Singapore so I knew access would be difficult. I arrived in Dong Dang two days before the arrival of Kim and preparations were tricky Ð undercover police officers stopped me every time I pulled out my camera. One day before his arrival I, along with the worldÕs media, began negotiating with media liaison officers about staking out the best spots. No one had approval from security yet. We positioned ourselves 70 meters opposite the gate of the train station. Producers sent their assistants to buy ladders. I rushed back to my hotel and borrowed one Ð but Japan's and Korea's were higher. By the afternoon no one dared abandon their spot. His expected arrival was early morning, so we camped outside the Dong Dang train station in the cold next to a wall of ladders. When he arrived, Kim Jung Un shook hands with Vietnamese delegates and waved to the media as he exited the train station. The level of access was unprecedented. After he got into his limousine, I no longer had a good vantage point from my ladder, so I instinctively ran to the side of his car which was surrounded by bodyguards. Just before the window closed, I captured his expression. I called it 'Kim Jong Un's Mona Lisa Smile'." REUTERS/Athit Perawongmetha/File Photo SEARCH "POY STORIES 2019" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES. TPX IMAGES OF THE DAY

Since 1945, more than 2,000 nuclear explosive tests have been carried out around the world.

Police are seen outside Villa Elfik Strand at Lidingo, outside Stockholm, Sweden, October 5, 2019, where U.S. top negotiator on North Korea, Stephen Biegun is expected to meet North Korea's chief nuclear negotiator, Kim Myong Gil. REUTERS/Anna Ringstrom

Police are seen outside Villa Elfik Strand at Lidingo, outside Stockholm, Sweden, October 5, 2019, where U.S. top negotiator on North Korea, Stephen Biegun is expected to meet North Korea's chief nuclear negotiator, Kim Myong Gil. REUTERS/Anna Ringstrom

Police are seen outside Villa Elfik Strand at Lidingo, outside Stockholm, Sweden, October 5, 2019, where U.S. top negotiator on North Korea, Stephen Biegun is expected to meet North Korea's chief nuclear negotiator, Kim Myong Gil. REUTERS/Anna Ringstrom

Members of the press wait outside Villa Elfik Strand at Lidingo, outside Stockholm, Sweden, October 5, 2019, where U.S. top negotiator on North Korea, Stephen Biegun is expected to meet North Korea's chief nuclear negotiator, Kim Myong Gil. REUTERS/Anna Ringstrom

Members of the press wait outside Villa Elfik Strand at Lidingo, outside Stockholm, Sweden, October 5, 2019, where U.S. top negotiator on North Korea, Stephen Biegun is expected to meet North Korea's chief nuclear negotiator, Kim Myong Gil. REUTERS/Anna Ringstrom

All nuclear tests and ballistic missile launches under the leadership of Kim Jong Il and Kim Jong Un. Launch data as of August 15, 2019.

Pruebas nucleares y de misiles balísticos lanzadas bajo el liderazgo de Kim Jong Il and Kim Jong Un.

UPDATE July 31 All nuclear tests and ballistic missile launches under the leadership of Kim Jong Il and Jim Jong Un.

FILE PHOTO: North Korea's ambassador to the United Nations Han Tae Song attends the Conference of Disarmament at the United Nations in Geneva, Switzerland, February 27, 2018. REUTERS/Denis Balibouse/File Photo

U.S. Secretary of State Mike Pompeo stands with Vice Chairman of the North Korean Workers' Party Committee Kim Yong Chol, North Korea's lead negotiator in nuclear diplomacy with the United States, for talks aimed at clearing the way for a second U.S.-North Korea summit as they meet at a hotel in Washington, U.S., January 18, 2019. REUTERS/Joshua Roberts

Vice Chairman of the North Korean Workers' Party Committee Kim Yong Chol, North Korea's lead negotiator in nuclear diplomacy with the United States, waves as he meets with U.S. Secretary of State Mike Pompeo (reflected in background 2ndL) for talks aimed at clearing the way for a second U.S.-North Korea summit in Washington, U.S., January 18, 2019. REUTERS/Joshua Roberts

U.S. Secretary of State Mike Pompeo escorts Vice Chairman of the North Korean Workers' Party Committee Kim Yong Chol, North Korea's lead negotiator in nuclear diplomacy with the United States, into talks aimed at clearing the way for a second U.S.-North Korea summit as they meet at a hotel in Washington, U.S., January 18, 2019. REUTERS/Joshua Roberts

U.S. Secretary of State Mike Pompeo meets with Vice Chairman of the North Korean Workers' Party Committee Kim Yong Chol, North Korea's lead negotiator in nuclear diplomacy with the United States, for talks aimed at clearing the way for a second U.S.-North Korea summit as they meet at a hotel in Washington, U.S., January 18, 2019. REUTERS/Joshua Roberts

U.S. Secretary of State Mike Pompeo greets Vice Chairman of the North Korean Workers' Party Committee Kim Yong Chol, North Korea's lead negotiator in nuclear diplomacy with the United States, as they start talks aimed at clearing the way for a second U.S.-North Korea summit while meeting at a hotel in Washington, U.S., January 18, 2019. REUTERS/Joshua Roberts

U.S. Secretary of State Mike Pompeo poses with Vice Chairman of the North Korean Workers' Party Committee Kim Yong Chol, North Korea's lead negotiator in nuclear diplomacy with the United States and U.S. Special Representative for North Korea Stephen Biegun as they start talks aimed at clearing the way for a second U.S.-North Korea summit while meeting at a hotel in Washington, U.S., January 18, 2019. REUTERS/Joshua Roberts

U.S. Secretary of State Mike Pompeo poses with Vice Chairman of the North Korean Workers' Party Committee Kim Yong Chol, North Korea's lead negotiator in nuclear diplomacy with the United States, as they start talks aimed at clearing the way for a second U.S.-North Korea summit while meeting at a hotel in Washington, U.S., January 18, 2019. REUTERS/Joshua Roberts

U.S. Secretary of State Mike Pompeo escorts Vice Chairman of the North Korean Workers' Party Committee Kim Yong Chol, North Korea's lead negotiator in nuclear diplomacy with the United States, into talks aimed at clearing the way for a second U.S.-North Korea summit as they meet at a hotel in Washington, U.S., January 18, 2019. REUTERS/Joshua Roberts

U.S. Secretary of State Mike Pompeo escorts Vice Chairman of the North Korean Workers' Party Committee Kim Yong Chol, North Korea's lead negotiator in nuclear diplomacy with the United States, into talks aimed at clearing the way for a second U.S.-North Korea summit as they meet at a hotel in Washington, U.S., January 18, 2019. REUTERS/Joshua Roberts

U.S. Secretary of State Mike Pompeo poses with Vice Chairman of the North Korean Workers' Party Committee Kim Yong Chol, North Korea's lead negotiator in nuclear diplomacy with the United States, for talks aimed at clearing the way for a second U.S.-North Korea summit as they meet at a hotel in Washington, U.S., January 18, 2019. REUTERS/Joshua Roberts

U.S. Secretary of State Mike Pompeo poses with Vice Chairman of the North Korean Workers' Party Committee Kim Yong Chol, North Korea's lead negotiator in nuclear diplomacy with the United States, for talks aimed at clearing the way for a second U.S.-North Korea summit as they meet at a hotel in Washington, U.S., January 18, 2019. REUTERS/Joshua Roberts

Massimo Aparo, IAEA Deputy Director General and Head of the Department of Safeguards, talks with South Korean Deputy Foreign Minister for Multilateral and Global Affairs Kang Jeong-sik before their regular high-level policy consultative meeting at the Foreign Ministry in Seoul, South Korea, November 26, 2018. Ahn Young-joon/Pool via REUTERS

Massimo Aparo, IAEA Deputy Director General and Head of the Department of Safeguards, shakes hands with South Korean Deputy Foreign Minister for Multilateral and Global Affairs Kang Jeong-sik during their regular high-level policy consultative meeting at the Foreign Ministry in Seoul, South Korea, November 26, 2018. Ahn Young-joon/Pool via REUTERS

Massimo Aparo, IAEA Deputy Director General and Head of the Department of Safeguards, is greeted by South Korean Deputy Foreign Minister for Multilateral and Global Affairs Kang Jeong-sik during their regular high-level policy consultative meeting at the Foreign Ministry in Seoul, South Korea, November 26, 2018. Ahn Young-joon/Pool via REUTERS

U.S. special representative for North Korea Stephen Biegun talks to South Korea's Special Representative for Korean Peninsula Peace and Security Affairs Lee Do-hoon during a meeting to discuss North Korea nuclear issues at the Foreign Ministry in Seoul, South Korea, October 29, 2018. Ahn Young-joon/Pool via REUTERS

U.S. special representative for North Korea Stephen Biegun shakes hands with South Korea's Special Representative for Korean Peninsula Peace and Security Affairs Lee Do-hoon during a meeting to discuss North Korea nuclear issues at the Foreign Ministry in Seoul, South Korea, October 29, 2018. Ahn Young-joon/Pool via REUTERS

South Korean Foreign Minister Kang Kyung-wha talks to U.S. special representative for North Korea Stephen Biegun during a meeting to discuss North Korea nuclear issues at the Foreign Ministry in Seoul, South Korea, October 29, 2018. Ahn Young-joon/Pool via REUTERS

South Korean Foreign Minister Kang Kyung-wha and U.S. special representative for North Korea Stephen Biegun arrive to hold their meeting to discuss North Korea nuclear issues at the Foreign Ministry in Seoul, South Korea, October 29, 2018. Ahn Young-joon/Pool via REUTERS

South Korean Foreign Minister Kang Kyung-wha shakes hands with U.S. special representative for North Korea Stephen Biegun at their meeting to discuss North Korea nuclear issues at the Foreign Ministry in Seoul, South Korea, October 29, 2018. Ahn Young-joon/Pool via REUTERS

U.S. Secretary of State Mike Pompeo arrives for the meeting with South Korean President Moon Jae-in at the presidential Blue House in Seoul, South Korea, October 7, 2018. REUTERS/Kim Hong-Ji/Pool

U.S. Secretary of State Mike Pompeo talks with South Korean President Moon Jae-in during their meeting at the presidential Blue House in Seoul, South Korea, October 7, 2018. REUTERS/Kim Hong-Ji/Pool

U.S. Secretary of State Mike Pompeo meets with South Korean Foreign Minister Kang Kyung-wha before meeting with South Korean President Moon Jae-in at the presidential Blue House in Seoul, South Korea, October 7, 2018. REUTERS/Kim Hong-Ji/Pool