Full coverage: Xi Visits Czech Republic, Attends Nuclear Security Summit

A US official commented on the global significance of deeper nuclear security cooperation between China and the United States. Scott Roecker, Director for the Defense Threat Reduction Agency, said their Joint Statement on Nuclear Security Cooperation was one of the highlights of this year's summit. He also stressed the importance of China's contribution to global nuclear security.

"Our bilateral relationship with China is one of the most important in the world. Obviously China has a very important role to play as it relates to security nuclear materials. We've had robust engagement with China for more than a decade on best practices exchanges on important topics on security nuclear material. Just two weeks ago, China opened a center of excellence which will be a forum where these best practices can be exchanged and an opportunity for China to share that throughout the region as well, and demonstrate its leadership on nuclear security to the region," Roecker said.