Chung Eui-yong, head of the presidential National Security Office, Suh Hoon, the chief of the South's National Intelligence Service, and other delegates arrive at a military airport in Seongnam, South Korea, March 6, 2018. REUTERS/Song Kyung-Seok/Pool 

Chung Eui-yong, head of the presidential National Security Office, Suh Hoon, the chief of the South's National Intelligence Service, and other delegates (not pictured) arrive at a military airport in Seongnam, South Korea, March 6, 2018. REUTERS/Song Kyung-Seok/Pool 

Chung Eui-yong, head of the presidential National Security Office, Suh Hoon, the chief of the South's National Intelligence Service, and other delegates (not pictured) arrive at a military airport in Seongnam, South Korea, March 6, 2018. REUTERS/Song Kyung-Seok/Pool 

Chung Eui-yong, head of the presidential National Security Office, Suh Hoon, chief of the South's National Intelligence Service, and other members of South Korean delegation pose before boarding an aircraft as they leave for Pyongyang at a military airport in Seongnam, south of Seoul, South Korea March 5, 2018. REUTERS/Jung Yeon-je/Pool 

Chung Eui-yong, head of the presidential National Security Office, walks to board an aircraft as they leave for Pyongyang at a military airport in Seongnam, south of Seoul, South Korea March 5, 2018. REUTERS/Jung Yeon-je/Pool 

Chung Eui-yong, head of the presidential National Security Office, and Suh Hoon, chief of the South's National Intelligence Service, talk before boarding an aircraft as they leave for Pyongyang at a military airport in Seongnam, south of Seoul, South Korea March 5, 2018. REUTERS/Jung Yeon-je/Pool 

A South Korean delegation boards an aircraft as they leave for Pyongyang at a military airport in Seongnam, south of Seoul, South Korea March 5, 2018. REUTERS/Jung Yeon-je/Pool 

Chung Eui-yong, head of the presidential National Security Office, and Suh Hoon, chief of the South's National Intelligence Service, talk before boarding an aircraft as they leave for Pyongyang at a military airport in Seongnam, south of Seoul, South Korea March 5, 2018. REUTERS/Jung Yeon-je/Pool 

The logo of SK Hynix is seen at its headquarters in Seongnam, South Korea, April 25, 2016. REUTERS/Kim Hong-Ji 

Employee walks past the logo of SK Hynix at its headquarters in Seongnam, South Korea, April 25, 2016. REUTERS/Kim Hong-Ji 

The logo of SK Hynix is seen at its headquarters in Seongnam, South Korea, April 25, 2016. REUTERS/Kim Hong-Ji 

The logos of SK Hynix are seen as a security personnel stands guard at its headquarters in Seongnam, South Korea, April 25, 2016. REUTERS/Kim Hong-Ji 

Employees talk in front of the logo of SK Hynix at its headquarters in Seongnam, South Korea, April 25, 2016. REUTERS/Kim Hong-Ji 

Employees walk past identification systems bearing the logos of SK Hynix at its headquarters in Seongnam, South Korea, April 25, 2016. REUTERS/Kim Hong-Ji 

The logos of SK Hynix is seen at its headquarters in Seongnam, South Korea, April 25, 2016. REUTERS/Kim Hong-Ji 

Employee walk past the logo of SK Hynix at its headquarters in Seongnam, South Korea, April 25, 2016. REUTERS/Kim Hong-Ji 

Egypt's President Abdel Fattah al-Sisi (R) signs his name in the visitors' book as South Korean President Park Geun-hye (L) looks on, prior to their meeting at the presidential house in Seoul, South Korea, March 3, 2016. REUTERS/Jeon Heon-kyun/Pool 

Egypt's President Abdel Fattah al-Sisi (L) and South Korea's President Park Geun-Hye (R) pose for photographers prior their meeting at the presidential house in Seoul, South Korea, March 3, 2016. REUTERS/Jeon Heon-kyun/Pool 

Egypt's President Abdel Fattah al-Sisi (L) and South Korea's President Park Geun-Hye (R) pose for photographers prior their meeting at the presidential house in Seoul, South Korea, March 3, 2016. REUTERS/Jeon Heon-kyun/Pool 

Japanese Prime Minister Shinzo Abe waves as he leaves Seoul Air Base in Seongnam, South Korea, November 2, 2015. South Korean President Park Geun-hye and Abe held their first formal bilateral talks on Monday since both leaders took office, seeking to move beyond a bitter wartime history that has plagued ties between two of Washington's key Asian allies. REUTERS/Kim Hong-Ji 

Japanese Prime Minister Shinzo Abe waves as he leaves Seoul Air Base in Seongnam, South Korea, November 2, 2015. South Korean President Park Geun-hye and Abe held their first formal bilateral talks on Monday since both leaders took office, seeking to move beyond a bitter wartime history that has plagued ties between two of Washington's key Asian allies. REUTERS/Kim Hong-Ji 

Chinese Premier Li Keqiang (C) arrives as he leaves Seoul Air Base in Seongnam, South Korea, November 2, 2015. REUTERS/Kim Hong-Ji 

Chinese Premier Li Keqiang (3rd R) shakes hands with motorcycle policemen as he leaves Seoul Air Base in Seongnam, South Korea, November 2, 2015. REUTERS/Kim Hong-Ji 

Chinese Premier Li Keqiang waves as he leaves Seoul Air Base in Seongnam, South Korea, November 2, 2015. REUTERS/Kim Hong-Ji 

Chinese Premier Li Keqiang waves as he leaves Seoul Air Base in Seongnam, South Korea, November 2, 2015. REUTERS/Kim Hong-Ji 

Japanese Prime Minister Shinzo Abe (C) walks with South Korean First Vice Foreign Minister Lim Sung-nam (R) upon his arrival at Seoul Air Base in Seongnam, South Korea, November 1, 2015. REUTERS/Kim Hong-Ji 

Japanese Prime Minister Shinzo Abe (2nd R) is greeted by South Korean First Vice Foreign Minister Lim Sung-nam (R) upon his arrival at Seoul Air Base in Seongnam, South Korea, November 1, 2015. REUTERS/Kim Hong-Ji 

Japanese Prime Minister Shinzo Abe (C) walks with South Korean First Vice Foreign Minister Lim Sung-nam (R) upon his arrival at Seoul Air Base in Seongnam, South Korea, November 1, 2015. REUTERS/Kim Hong-Ji 

Japanese Prime Minister Shinzo Abe (L) walks with South Korean First Vice Foreign Minister Lim Sung-nam upon his arrival at Seoul Air Base in Seongnam, South Korea, November 1, 2015. REUTERS/Kim Hong-Ji 

Japanese Prime Minister Shinzo Abe arrives at Seoul Air Base in Seongnam, South Korea, November 1, 2015. REUTERS/Kim Hong-Ji 

Chinese Premier Li Keqiang waves upon his arrival at Seoul Air Base in Seongnam, South Korea, October 31, 2015. REUTERS/Kim Hong-Ji 

Chinese Premier Li Keqiang arrives at Seoul Air Base in Seongnam, South Korea, October 31, 2015. REUTERS/Kim Hong-Ji 

Chinese Premier Li Keqiang waves upon his arrival at Seoul Air Base in Seongnam, South Korea, October 31, 2015. REUTERS/Kim Hong-Ji 

Chinese Premier Li Keqiang waves upon his arrival at Seoul Air Base in Seongnam, South Korea, October 31, 2015. REUTERS/Kim Hong-Ji 

Ahn Yoon-joon, 86, who has been selected as one of 90 participants of reunion, poses for photographs during an interview with Reuters in Seongnam, South Korea, October 13, 2015. The two Koreas, bitter rivals that remain in a technical state of war, agreed to hold family reunions for the first time since February 2014 after negotiating the end of a standoff at their heavily militarized border. The reunion of 90 South Koreans and 96 North Koreans, the 20th of its kind, will be held at a resort in the North, mostly in a large ballroom under the watchful eye of officials. The reunions are politically important for the South, where 66,000 people are on a waiting list to see long-lost relatives, a number that is shrinking fast, while the North also seeks to maximize their domestic propaganda value. Picture taken October 13, 2015. REUTERS/Kim Hong-Ji 

Ahn Yoon-joon, 86, who has been selected as one of 90 participants of reunion, holds a confirmation document of whereabouts of his family members living in North Korea, speaks during an interview with Reuters in Seongnam, South Korea, October 13, 2015. The two Koreas, bitter rivals that remain in a technical state of war, agreed to hold family reunions for the first time since February 2014 after negotiating the end of a standoff at their heavily militarized border. The reunion of 90 South Koreans and 96 North Koreans, the 20th of its kind, will be held at a resort in the North, mostly in a large ballroom under the watchful eye of officials. The reunions are politically important for the South, where 66,000 people are on a waiting list to see long-lost relatives, a number that is shrinking fast, while the North also seeks to maximize their domestic propaganda value. Picture taken October 13, 2015. REUTERS/Kim Hong-Ji 

U.S. Secretary of State John Kerry salutes as he boards his airplane prior to departure from Seoul Air Base in Seongnam, south of Seoul, South Korea, May 18, 2015. REUTERS/Saul Loeb/POOL 

U.S. Secretary of State John Kerry walks past an honor guard as he boards his airplane prior to departure from Seoul Air Base in Seongnam, south of Seoul, South Korea, May 18, 2015. REUTERS/Saul Loeb/Pool 

U.S. Secretary of State John Kerry walks past an honor guard as he boards his airplane prior to departure from Seoul Air Base in Seongnam, south of Seoul, South Korea, May 18, 2015. REUTERS/Saul Loeb/Pool 

U.S. Secretary of State John Kerry arrives at a military airport in Seongnam, South Korea, May 17, 2015. REUTERS/Kim Hong-Ji 

U.S. Secretary of State John Kerry (center R) is greeted by U.S. ambassador to South Korea Mark Lippert (center L) upon his arrival at a military airport in Seongnam, South Korea, May 17, 2015. REUTERS/Kim Hong-Ji 

U.S. Secretary of State John Kerry arrives at a military airport in Seongnam, South Korea, May 17, 2015. REUTERS/Kim Hong-Ji 

U.S. Secretary of State John Kerry arrives at a military airport in Seongnam, South Korea, May 17, 2015. REUTERS/Kim Hong-Ji 

U.S. Secretary of State John Kerry waves upon his arrival at a military airport in Seongnam, South Korea, May 17, 2015. REUTERS/Kim Hong-Ji 

U.S. Secretary of State John Kerry (R) arrives as U.S. ambassador to South Korea Mark Lippert stands next to him at a military airport in Seongnam, South Korea, May 17, 2015. REUTERS/Kim Hong-Ji 

U.S. Secretary of State John Kerry arrives at a military airport in Seongnam, South Korea, May 17, 2015. REUTERS/Kim Hong-Ji 

A police official examines the scene of an accident at a shopping district in Seongnam October 17, 2014. Fourteen people were killed at a open-air pop concert in South Korea on Friday when the cover of a ventilation shaft they were standing on gave way, officials and media said. REUTERS/Kim Hong-Ji (SOUTH KOREA - Tags: DISASTER) 

Police officials examine the scene of an accident at a shopping district in Seongnam October 17, 2014. Fourteen people were killed at a open-air pop concert in South Korea on Friday when the cover of a ventilation shaft they were standing on gave way, officials and media said. REUTERS/Kim Hong-Ji (SOUTH KOREA - Tags: DISASTER SOCIETY TPX IMAGES OF THE DAY) 

Pope Francis (front R) shakes hands with bishops before boarding his plane at Seoul Air Base in Seongnam August 18, 2014. Francis on Monday called for peace and reconciliation on the divided Korean peninsula, wrapping-up a five day trip to South Korea and the first papal visit to Asia in 15 years. REUTERS/Kim Hong-Ji (SOUTH KOREA - Tags: POLITICS RELIGION) 

Pope Francis (R), wearing a yellow ribbon, the symbol of tribute for Sewol ferry disaster victims, shakes hands with bishops before boarding his plane at Seoul Air Base in Seongnam August 18, 2014. Francis on Monday called for peace and reconciliation on the divided Korean peninsula, wrapping-up a five day trip to South Korea and the first papal visit to Asia in 15 years. REUTERS/Kim Hong-Ji (SOUTH KOREA - Tags: POLITICS RELIGION) 

Pope Francis (C) waves before boarding his plane at Seoul Air Base in Seongnam August 18, 2014. Francis on Monday called for peace and reconciliation on the divided Korean peninsula, wrapping-up a five day trip to South Korea and the first papal visit to Asia in 15 years. REUTERS/Kim Hong-Ji (SOUTH KOREA - Tags: POLITICS RELIGION) 

Pope Francis arrives at Seoul Air Base in Seongnam August 18, 2014. Francis on Monday called for peace and reconciliation on the divided Korean peninsula, wrapping-up a five day trip to South Korea and the first papal visit to Asia in 15 years. REUTERS/Kim Hong-Ji (SOUTH KOREA - Tags: POLITICS RELIGION) 

Pope Francis waves upon his arrival at Seoul Air Base, as South Korean President Park Geun-hye (L) smiles, in Seongnam, August 14, 2014. Pope Francis sent an unprecedented message of good will to China on Thursday before touching down in Seoul, but the first papal trip to Asia in 15 years got off to a shaky start with the news some Chinese had been barred from joining a youth celebration. REUTERS/Ahn Young-joon/Pool (SOUTH KOREA - Tags: POLITICS RELIGION) 

Pope Francis is seen in his popemobile car as South Korean President Park Geun-hye (C) watches upon his arrival at Seoul Air Base in Seongnam August 14, 2014. Pope Francis arrived in the South Korean capital Seoul on Thursday after sending an unprecedented message of good will to China as he flew over the country that does not allow its Catholics to recognise his authority. Francis will spend five days in South Korea, meeting some of the country's five million Catholics on the first trip by a pontiff to Asia since 1999. REUTERS/Ahn Young-joon/Pool (SOUTH KOREA - Tags: POLITICS RELIGION) 

Pope Francis (centre L) and South Korean President Park Geun-hye inspect the honour guard upon his arrival at Seoul Air Base in Seongnam August 14, 2014. Pope Francis arrived in the South Korean capital Seoul on Thursday after sending an unprecedented message of good will to China as he flew over the country that does not allow its Catholics to recognize his authority. REUTERS/Ahn Young-joon/Pool (SOUTH KOREA - Tags: POLITICS RELIGION) 

Pope Francis leaves the plane upon his arrival at Seoul Air Base in Seongnam August 14, 2014.
Pope Francis arrived in the South Korean capital Seoul on Thursday after sending an unprecedented message of good will to China as he flew over the country that does not allow its Catholics to recognize his authority. REUTERS/Ahn Young-joon/Pool (SOUTH KOREA - Tags: POLITICS RELIGION) 

Pope Francis (C) is escorted by South Korean President Park Geun-hye upon his arrival at Seoul Air Base in Seongnam August 14, 2014. Pope Francis arrived in the South Korean capital Seoul on Thursday after sending an unprecedented message of good will to China as he flew over the country that does not allow its Catholics to recognize his authority. REUTERS/Ahn Young-joon/Pool (SOUTH KOREAPOLITICS RELIGION) 

Pope Francis is greeted by well-wishers upon his arrival at Seoul Air Base in Seongnam August 14, 2014. Pope Francis arrived in the South Korean capital Seoul on Thursday after sending an unprecedented message of good will to China as he flew over the country that does not allow its Catholics to recognize his authority. REUTERS/Ahn Young-joon/Pool (SOUTH KOREA - Tags: POLITICS RELIGION) 

Pope Francis (C) is greeted by well-wishers as he is flanked by South Korean President Park Geun-hye (2nd R) upon his arrival at Seoul Air Base in Seongnam August 14, 2014. Pope Francis arrived in the South Korean capital Seoul on Thursday, where he will spend five days travelling around the country and meeting some of South Korea's five million Catholics on the first trip by a pontiff to Asia since 1999. REUTERS/Ahn Young-joon/Pool (SOUTH KOREA - Tags: POLITICS RELIGION TPX IMAGES OF THE DAY) 

Pope Francis (centre L) and South Korea's President Park Geun-hye inspect the honour guard upon his arrival at Seoul Air Base in Seongnam August 14, 2014. Pope Francis arrived in the South Korean capital Seoul on Thursday, where he will spend five days travelling around the country and meeting some of South Korea's five million Catholics on the first trip by a pontiff to Asia since 1999. REUTERS/Ahn Young-joon/Pool (SOUTH KOREA - Tags: POLITICS RELIGION)