Chinese Premier Li Keqiang (R) shakes hands with Serbian President Tomislav Nikolic (L) at the Great Hall of People in Beijing, China March 31, 2017. At the invitation of President Xi Jinping, President of the Republic of Serbia Tomislav Nikolic will pay a state visit to China from March 28 to March 31. REUTERS/Lintao Zhang/Pool 

Chinese Premier Li Keqiang (R) shakes hands with Serbian President Tomislav Nikolic (L) at the Great Hall of People in Beijing, China March 31, 2017. At the invitation of President Xi Jinping, President of the Republic of Serbia Tomislav Nikolic will pay a state visit to China from March 28 to March 31. REUTERS/Lintao Zhang/Pool 

Chinese Premier Li Keqiang arrives to meet with Serbian President Tomislav Nikolic at the Great Hall of People in Beijing, China March 31, 2017. At the invitation of President Xi Jinping, President of the Republic of Serbia Tomislav Nikolic will pay a state visit to China from March 28 to March 31. REUTERS/Lintao Zhang/Pool 

Serbian President Tomislav Nikolic meets with Chinese Premier Li Keqiang (not pictured) at the Great Hall of People in Beijing, China March 31, 2017. At the invitation of President Xi Jinping, President of the Republic of Serbia Tomislav Nikolic will pay a state visit to China from March 28 to March 31. REUTERS/Lintao Zhang/Pool 

Chinese Premier Li Keqiang (2nd R) meets with Serbian President Tomislav Nikolic (2nd L) at the Great Hall of People in Beijing, China March 31, 2017. At the invitation of President Xi Jinping, President of the Republic of Serbia Tomislav Nikolic will pay a state visit to China from March 28 to March 31. REUTERS/Lintao Zhang/Pool 

Chinese Premier Li Keqiang (R) shakes hands with Serbian President Tomislav Nikolic (L) at the Great Hall of People in Beijing, China March 31, 2017. At the invitation of President Xi Jinping, President of the Republic of Serbia Tomislav Nikolic will pay a state visit to China from March 28 to March 31. REUTERS/Lintao Zhang/Pool 

China's President Xi Jinping and his wife Peng Liyuan attend a welcoming ceremony for Serbia's President Tomislav Nikolic (not pictured) at the Great Hall of the People in Beijing, China, March 30, 2017. Picture taken March 30, 2017. REUTERS/Thomas Peter 

China's President Xi Jinping and his wife Peng Liyuan attend a welcoming ceremony for Serbia's President Tomislav Nikolic (not pictured) at the Great Hall of the People in Beijing, China, March 30, 2017. Picture taken March 30, 2017. REUTERS/Thomas Peter 

China's President Xi Jinping and his wife Peng Liyuan attend a welcoming ceremony for Serbia's President Tomislav Nikolic (not pictured) at the Great Hall of the People in Beijing, China, March 30, 2017. Picture taken March 30, 2017. REUTERS/Thomas Peter 

Serbian President Tomislav Nikolic meets with Chinese President Xi Jinping at the Great Hall of the People in Beijing, China March 30, 2017. REUTERS/Lintao Zhang/Pool 

Chinese President Xi Jinping (R) shakes hands with Serbian President Tomislav Nikolic during a honorary citizenship ceremony for Tomislav Nikolic at the Great Hall of the People in Beijing, China March 30, 2017. REUTERS/Lintao Zhang/Pool 

Chinese President Xi Jinping (R) and Serbian President Tomislav Nikolic attend a honorary citizenship ceremony for Tomislav Nikolic at the Great Hall of the People in Beijing, China March 30, 2017. REUTERS/Lintao Zhang/Pool 

Chinese President Xi Jinping meets with Serbian President Tomislav Nikolic at the Great Hall of the People in Beijing, China March 30, 2017. REUTERS/Lintao Zhang/Pool 

Serbian President Tomislav Nikolic meets with Chinese President Xi Jinping at the Great Hall of the People in Beijing, China March 30, 2017. REUTERS/Lintao Zhang/Pool 

Chinese President Xi Jinping meets with Serbian President Tomislav Nikolic at the Great Hall of the People in Beijing, China March 30, 2017. REUTERS/Lintao Zhang/Pool 

Chinese President Xi Jinping meets with Serbian President Tomislav Nikolic at the Great Hall of the People, in Beijing, China March 30, 2017. REUTERS/Lintao Zhang/Pool 

Members of a military band enter the Great Hall of the People before the welcoming ceremony for Serbia's President Tomislav Nikolic in Beijing, China, March 30, 2017. REUTERS/Thomas Peter 

A military band waits for the start of the welcoming ceremony for Serbia's President Tomislav Nikolic at the Great Hall of the People in Beijing, China March 30, 2017. REUTERS/Thomas Peter 

Members of the Chinese honour guard march before a welcoming ceremony for Serbia's President Tomislav Nikolic at the Great Hall of the People in Beijing, China, March 30, 2017. REUTERS/Thomas Peter 

China's President Xi Jinping and Serbia's President Tomislav Nikolic inspect the honour guard during a welcoming ceremony at the Great Hall of the People in Beijing, China, March 30, 2017. REUTERS/Thomas Peter 

Children greet Serbia's President Tomislav Nikolic and China's President Xi Jinping during a welcoming ceremony at the Great Hall of the People in Beijing, China, March 30, 2017. REUTERS/Thomas Peter 

China's President Xi Jinping meets Serbia's President Tomislav Nikolic and his wife Dragica Nikolic at the Great Hall of the People in Beijing, China, March 30, 2017. REUTERS/Thomas Peter 

China's President Xi Jinping and Serbia's President Tomislav Nikolic inspect the honour guard during a welcoming ceremony at the Great Hall of the People in Beijing, China, March 30, 2017. REUTERS/Thomas Peter 

China's President Xi Jinping and Serbia's President Tomislav Nikolic inspect the honour guard during a welcoming ceremony at the Great Hall of the People in Beijing, China, March 30, 2017. REUTERS/Thomas Peter 

China's President Xi Jinping meets Serbia's President Tomislav Nikolic at the Great Hall of the People in Beijing, China, March 30, 2017. REUTERS/Thomas Peter 

China's President Xi Jinping meets Serbia's President Tomislav Nikolic at the Great Hall of the People in Beijing, China, March 30, 2017. REUTERS/Thomas Peter 

China's President Xi Jinping meets Serbia's President Tomislav Nikolic at the Great Hall of the People in Beijing, China, March 30, 2017. REUTERS/Thomas Peter 

China's President Xi Jinping meets Serbia's President Tomislav Nikolic at the Great Hall of the People in Beijing, China March 30, 2017. REUTERS/Thomas Peter 

China's President Xi Jinping meets Serbia's President Tomislav Nikolic at the Great Hall of the People in Beijing, China, March 30, 2017. REUTERS/Thomas Peter 

Serbia's President Tomislav Nikolic and his wife Dragica Nikolic are welcomed by Portugal's President Marcelo Rebelo de Sousa (R) at Jeronimos Monastery in Lisbon, Portugal January 25, 2017. REUTERS/Rafael Marchante 

Serbia's President Tomislav Nikolic and his wife Dragica Nikolic are welcomed by Portugal's President Marcelo Rebelo de Sousa (R) at Jeronimos Monastery in Lisbon, Portugal January 25, 2017. REUTERS/Rafael Marchante 

Serbia's President Tomislav Nikolic (C) and his wife Dragica Nikolic are welcomed by Portugal's President Marcelo Rebelo de Sousa at Jeronimos Monastery in Lisbon, Portugal January 25, 2017. REUTERS/Rafael Marchante 

Serbia's President Tomislav Nikolic (C) and his wife Dragica Nikolic are welcomed by Portugal's President Marcelo Rebelo de Sousa at Jeronimos Monastery in Lisbon, Portugal January 25, 2017. REUTERS/Rafael Marchante 

Serbia's President Tomislav Nikolic (L) and his wife Dragica Nikolic pose for the photographers with Portugal's President Marcelo Rebelo de Sousa at Jeronimos Monastery in Lisbon, Portugal January 25, 2017. REUTERS/Rafael Marchante 

Serbia's President Tomislav Nikolic visits the tomb of Portuguese poet Luis de Camoes during the official welcome ceremony at Lisbon's Jeronimos Monastery, Portugal January 25, 2017. REUTERS/Rafael Marchante 

Serbia's President Tomislav Nikolic arrives for a meeting with his Portuguese counterpart Marcelo Rebelo de Sousa (not pictured) at Jeronimos Monastery in Lisbon, Portugal January 25, 2017. REUTERS/Rafael Marchante 

Serbia's President Tomislav Nikolic (L) is welcomed by his Portuguese counterpart Marcelo Rebelo de Sousa at Jeronimos Monastery in Lisbon, Portugal January 25, 2017. REUTERS/Rafael Marchante 

Serbia's President Tomislav Nikolic (L) is welcomed by his Portuguese counterpart Marcelo Rebelo de Sousa at Jeronimos Monastery in Lisbon, Portugal January 25, 2017. REUTERS/Rafael Marchante 

Serbia's President Tomislav Nikolic (L) is welcomed by his Portuguese counterpart Marcelo Rebelo de Sousa at Jeronimos Monastery in Lisbon, Portugal January 25, 2017. REUTERS/Rafael Marchante 

Serbia's President Tomislav Nikolic (L) is welcomed by his Portuguese counterpart Marcelo Rebelo de Sousa at Jeronimos Monastery in Lisbon, Portugal January 25, 2017. REUTERS/Rafael Marchante 

U.S. Vice President Joe Biden (L) and Serbia's President Tomislav Nikolic pose for media before their meeting in Belgrade, Serbia, August 16, 2016. REUTERS/Djordje Kojadinovic 

U.S. Vice President Joe Biden (L) and Serbia's President Tomislav Nikolic pose for picture before their meeting in Belgrade, Serbia, August 16, 2016. REUTERS/Djordje Kojadinovic 

Serbian President Tomislav Nikolic (R) awards Chinese President Xi Jinping with the medal of the Republic of Serbia after their meeting in Belgrade, Serbia June 18, 2016. REUTERS/Marko Djurica TPX IMAGES OF THE DAY

Serbian President Tomislav Nikolic awards Chinese President Xi Jinping with the medal of the Republic of Serbia after their meeting in Belgrade, Serbia June 18, 2016. REUTERS/Marko Djurica 

Chinese President Xi Jinping smiles after a joint news statement with Serbian President Tomislav Nikolic after their meeting in Belgrade, Serbia June 18, 2016. REUTERS/Marko Djurica 

Serbian President Tomislav Nikolic (R) awards Chinese President Xi Jinping with the medal of the Republic of Serbia after their meeting in Belgrade, Serbia June 18, 2016. REUTERS/Marko Djurica 

Serbian President Tomislav Nikolic (R) awards Chinese President Xi Jinping with the medal of the Republic of Serbia after their meeting in Belgrade, Serbia June 18, 2016. REUTERS/Marko Djurica 

Chinese President Xi Jinping (L) reviews the guard of honour with his Serbian counterpart Tomislav Nikolic during a welcoming ceremony in Belgrade, Serbia June 18, 2016. REUTERS/Marko Djurica 

Chinese President Xi Jinping's wife Peng Liyuan (L) and Serbian President Tomislav Nikolic's wife Dragica listen to their national anthems during a welcoming ceremony in Belgrade, Serbia June 18, 2016. REUTERS/Marko Djurica 

Chinese President Xi Jinping looks on during a meeting with his Serbian counterpart Tomislav Nikolic in Belgrade, Serbia June 18, 2016. REUTERS/Marko Djurica 

Chinese President Xi Jinping looks on during a meeting with his Serbian counterpart Tomislav Nikolic in Belgrade, Serbia June 18, 2016. REUTERS/Marko Djurica 

Chinese President Xi Jinping looks on during a meeting with his Serbian counterpart Tomislav Nikolic in Belgrade, Serbia June 18, 2016. REUTERS/Marko Djurica 

Chinese President Xi Jinping arrives for a meeting with his Serbian counterpart Tomislav Nikolic in Belgrade, Serbia June 18, 2016. REUTERS/Marko Djurica 

Chinese President Xi Jinping (L) shakes hands with his Serbian counterpart Tomislav Nikolic before their meeting in Belgrade, Serbia June 18, 2016. REUTERS/Marko Djurica 

Chinese President Xi Jinping (L) shakes hands with his Serbian counterpart Tomislav Nikolic before their meeting in Belgrade, Serbia June 18, 2016. REUTERS/Marko Djurica 

Chinese President Xi Jinping (L) reviews the guard of honour with his Serbian counterpart Tomislav Nikolic during a welcoming ceremony in Belgrade, Serbia June 18, 2016. REUTERS/Marko Djurica 

Chinese President Xi Jinping (L) reviews the guard of honour with his Serbian counterpart Tomislav Nikolic during a welcoming ceremony in Belgrade, Serbia June 18, 2016. REUTERS/Marko Djurica 

Chinese President Xi Jinping (L) reviews the guard of honour with his Serbian counterpart Tomislav Nikolic during a welcoming ceremony in Belgrade, Serbia June 18, 2016. REUTERS/Marko Djurica 

Serbia's President Tomislav Nikolic arrives for the Brdo-Brioni Process meeting, a gathering of political leaders from the Western Balkans, in Sarajevo, Bosnia and Herzegovina May 29, 2016. REUTERS/Dado Ruvic 

Serbia's President Tomislav Nikolic, Montenegro's President Filip Vujanovic, Slovenia's President Borut Pahor, Members of Bosnian Presidency Mladen Ivanic (4th L), Bakir Izetbegovic (6th L), Dragan Covic (5th R) Italy's President Sergio Mattarella, Croatia's President Kolinda Grabar-Kitarovic (4th R), Macedonia's President Gjorge Ivanov (3rd R), Albania's President Bujar Nishani (2nd R), Kosovo's President Hashim Thachi (R) pose for photo before the Brdo-Brioni Process meeting, a gathering of political leaders from the Western Balkans in Sarajevo, Bosnia and Herzegovina May 29, 2016. REUTERS/Dado Ruvic