Meanwhile, the US has warned North Korea could face yet more sanctions should Pyongyang not take steps to denuclearise.
The satellite evidence, coming from several US think tanks and testimony from the South Korean intelligence service, appears to show rapid progress has been made in rebuilding structures on the rocket launch pad at the Sohae site at Tongchang-ri.
Images last July appeared to show the North had begun to dismantle the site.
Sohae has been North Korea's main satellite launch facility since 2012. It has also been used for testing engines for missiles capable of reaching the US.
But it has never been used for testing the ballistic missiles which have been considered so provocative.
"The North Koreans likely see the rebuilding not as an active part of their missile programme, but of their civilian space programme - a distinction they have made repeatedly in the past," said Ms Town.
She said the rebuilding of structures at the site could signal a lack of trust in the negotiations process.
Analysis: Kim 'testing Trump's patience'
Laura Bicker, BBC News, Seoul
This is indeed worth watching and the rebuilding work does send a rather ominous signal. But I'm always cautious of extrapolating meaning from satellite images. We cannot make assumptions about what is being discussed in the corridors of power in Pyongyang based on building work at a remote satellite launch station.
This renewed activity may be Pyongyang's way of prodding Washington, just a little reminder to the Trump administration that it has the technology to build weapons and it will not give that up easily.
Most analysts believe it is more likely, at this stage, that Mr Kim is testing Mr Trump's boundaries and patience, rather than getting ready to test a ballistic missile.
If North Korea did go further than rebuilding a rocket test stand, and broke its pledge to stop testing missiles, it would risk the wrath of an unpredictable US president.
The impoverished state could be slapped with even more economic sanctions. Mr Kim has sold these denuclearisation talks at home, and is cultivating his statesman-like image abroad - is he really ready to put that all at risk?