North Korea has restored a part of a missile launch site that it had promised to dismantle after the first summit between President Donald Trump and North Korea's leader Kim Jong Un last year at Singapore, two U.S. think tanks reported Tuesday.

South Korea’s National Intelligence Service (NIS) told lawmakers at a briefing that activity was detected at the Tongchang-ri launch site. The roof and a door were among the things being fixed at the facility. The report comes just days after the failure of the second Trump-Kim summit at Hanoi.

The Center for Strategic and International Studies (CSIS) released a report that said, based on satellite imagery, North Korea is “pursuing a rapid rebuilding” at the site. At the same time, satellite images seen by 38 North --  a Washington based North Korea monitoring site -- showed some structures on the launch pad had been rebuilt sometime between Feb. 16 and March 2.

The satellite images showed that North Korea was rebuilding a vertical launch stand at the country's main site for long-range satellite launches. The site hasn't yet been used for the launch of intercontinental ballistic missiles (ICBM). Some U.S. officials believe that the civilian satellite launches are a cover for the military tests as the technologies used are similar.

Two construction cranes, several vehicles and supplies next to the engine test stand were seen in the images, along with those from the acivity at the launch pad's rail-mounted rocket transfer structure. 

The CSIS report said, “Activity is evident at the vertical engine test stand and the launch pad’s rail-mounted rocket transfer structure. Significantly, the environmental shelter on the umbilical tower, which are normally closed, have been opened to show the launch pad.”

Trump and Kim Jong Un held a second summit on denuclearization in Hanoi on Feb. 27 and 28. But no agreement was reached, especially on the elimination of North Korea’s nuclear weapons program.

After the Singapore summit in June 2018, the Sohae facility was inactive since Kim had made a commitment to Trump that North Korea will dismantle the launch facility.

A Washington think tank showed, in July 2018, that North Korea may have begun acting on its promise and begun the work of dismantling the building used to assemble space-launch vehicles and a nearby rocket engine test stand used to develop liquid fuel engines for ballistic missiles and space-launch vehicles.

In September, 2018, at a meeting with South Korean President Moon Jae-in, Kim had promised to close Sohae and allow international experts to observe the dismantling of the missile engine-testing site and a launch pad.

Analysts from CSIS believe that the current activity is a methodical and deliberate action to show North Korea’s determination to press ahead with nuclear weapon developmennt following the failure Hanoi summit. Trump had informed reporters at Hanoi that Kim had committed to continue to not conduct nuclear tests or ballistic missile tests.