In reports released by the Washington, D.C.-based Center for Strategic and International Studies, researcher Joseph Bermudez said maintenance and minor infrastructure improvements have been observed at some of the sites, despite the ongoing negotiations. North Korean leader Kim Jong Un and U.S. President Donald Trump pledged to work toward denuclearization at their landmark June summit in Singapore, but the agreement was short on specifics and negotiations have made little headway. Shortly after that summit, Trump tweeted that "there is no longer a Nuclear Threat from North Korea." North Korea declared its nuclear force "complete" and halted missile and nuclear bomb testing earlier this year, but U.S. and South Korean negotiators have yet to elicit from Pyongyang a concrete declaration of the size or scope of the weapons programs, or a promise to stop deploying its existing arsenal.