Nearly three weeks since North Korean ruler Kim Jong Un committed to complete denuclearization, multiple signs have emerged of expanding activity at his country's nuclear facilities.

If the reports are true, that would mean Kim has yet to take concrete steps to fulfill the pledge he made at a historic summit with U.S. President Donald Trump on June 12.

On Saturday, U.S. intelligence officials told NBC News that Pyongyang may have recently increased production of fuel for nuclear weapons at multiple secret sites. It's possible that Kim's government may be attempting to hide those pursuits as it seeks more concessions from the Trump administration, the officials continued.

Meanwhile last week, commercial satellite imagery from research group 38North — part of Washington-based think tank The Stimson Center — showed infrastructure upgrades at the Yongbyon Nuclear Scientific Research Center, which is located north of Pyongyang. The improvements include completed modifications to a plutonium production reactor’s cooling system, newly erected small buildings and continued construction on various support facilities, 38North said.

In a separate analysis released on June 21, 38North also published satellite imagery of the Sohae Satellite Launching Station that showed no signs of dismantlement. The station, used to test large rocket engines that are part of intercontinental ballistic missiles, is speculated to be the same engine site that Trump said North Korea was destroying on June 12.