Other satellite images show increased vehicle activities at a separate North Korean facility used to manufacture missiles, and rockets for satellite launches.
Experts are divided over Pyongyang's plans, but whatever its intentions, a launch would shatter the fragile US-North Korea relationship and revive the angry language that had stoked fears of a military conflict at the start of the Trump presidency.
"We see exactly what they're doing", he said. He said he has greatly improved USA relations with North Korea during his time in office.
North Korea must not use a possible rocket launch as leverage in negotiations with the U.S, a South Korean presidential adviser said Tuesday, saying such a move could be "catastrophic" for global diplomacy on its nuclear program. However, Trump told reporters that like the Singapore summit, Kim had committed not conducting nuclear or ballistic missile tests.
He said Mr Trump had proposed a "big deal" in the Hanoi summit under which North Korea would completely denuclearise and also give up its chemical and biological weapons.
Images of Samundong taken on February 22 showed cars and trucks at the site, as well as rail cars and cranes at a yard, U.S. news outlet NPR has reported.
The Chosun Ilbo reports that commercial satellite images have revealed trucks moving what are presumed to be missile components from an assembly facility in the suburbs of Pyongyang to the Tongchang-ri missile test site.
The site was dismantled in an apparent show of goodwill after Mr Trump's first summit with Mr Kim in June and the US President said he would be "very disappointed" if it was being rebuilt.
He continued, "Right now you have no testing, you have no nothing".
North Korea favours a more step-by-approach, with Kim proposing dismantling its Yongbyon nuclear complex in exchange for lifting the main sanctions - a notion Trump refused in Hanoi despite the vaunted "chemistry" between the pair.
"I would be very, very disappointed in Chairman Kim", Trump said on Wednesday.
He did admit, however, that Trump would be "pretty disappointed" if Kim Jong-un made a decision to test launch another missile. But the meeting collapsed over an impasse over how many weapons sites North Korea would shut down and the extent of economic sanctions relief the US would offer in return.