Chinese President Xi Jinping (4th R, front) poses for a group photo with other leaders attending the fourth Nuclear Security Summit in Washington DC, the United States, April 1, 2016. Photo: Xinhua

Chinese President Xi Jinping attends the fourth Nuclear Security Summit in Washington DC, the United States, April 1, 2016. Photo: Xinhua

Chinese President Xi Jinping attends the fourth Nuclear Security Summit in Washington DC, the United States, April 1, 2016. Photo: Xinhua

The fourth Nuclear Security Summit is held in Washington DC, the United States, April 1, 2016. Chinese President Xi Jinping attended the summit and delivered a speech. Photo: Xinhua