North Korea has begun rebuilding a rocket launch site that had been partially dismantled as a goodwill gesture after the first summit between Donald Trump and Kim Jong-un in June last year.

Satellite images show the reconstruction work was carried out shortly before their failed second summit in Hanoi last week, and their publication on Tuesday evening contributed to fears that the peace effort was in jeopardy.

The US national security adviser, John Bolton, warned that if the regime did not disarm, the already severe sanctions regime would be ramped up further.

Bolton told Fox Business Network that Washington was waiting to see whether Pyongyang was committed to giving up its “nuclear weapons program and everything associated with it”.

Commercial satellite image showing work on North Korea’s Sohae satellite launching station. Photograph: DigitalGlobe/Reuters

“If they’re not willing to do it, then I think President Trump has been very clear ... they’re not going to get relief from the crushing economic sanctions that have been imposed on them and we’ll look at ramping those sanctions up in fact,” he said.

The Hanoi summit was cut short last Thursday after Trump and Kim failed to agree on a deal trading nuclear disarmament for sanctions relief, but Trump administration officials were still claiming on Tuesday that progress had been made towards narrowing differences.

However, the new evidence that some of the confidence-building steps taken by Pyongyang after the first summit in Singapore have now been reversed, coupled with the pointed threat from Bolton, suggest Trump’s proudest foreign policy achievement is now in danger of unravelling.

After the South Korean intelligence service reported building work at the Sohae satellite launching station, two independent research websites published satellite photos showing that North Korean technicians had restored a moving structure that has been used to move space launch vehicles on rails to a launchpad and gantry. A stand used for testing rocket engines also showed signs of being rebuilt.

“On the launch pad, the rail-mounted transfer building is being reassembled,” the 38 North website, which tracks developments in North Korea, reported. “Two support cranes are observed at the building, the walls have been erected and a new roof added.

“At the engine test stand, it appears that the engine support structure is being reassembled. Two cranes are present and construction materials are spread across the stand’s apron.”

The Beyond Parallel website, which also published the satellite images, said: “This facility has been dormant since August 2018, indicating the current activity is deliberate and purposeful.”

Analysts stressed that the reconstruction work did not mean a new launch was imminent, and pointed out that the Sohae site had so far been used for satellite launches and not intercontinental ballistic missiles. However, some of the technology is the same, and for that reason the UN security council has banned North Korea from carrying out space launches.

North Korea experts speculated that the rebuilding work at Sohae was intended to send a message to Washington that relations could turn very sour again if progress was not made towards easing sanctions. Ankit Panda, a senior fellow at the Federation of American Scientists said in a tweet it could be a: “reminder of when times were worse and what stands to be lost if the process collapses”.

Commercial satellite image shows North Korea’s Sohae satellite launching station. Photograph: HANDOUT/Reuters

Trump and senior US officials had pointed to the dismantling of buildings at Sohae, coupled with the demolition of a tunnel at North Korea’s nuclear test site, as tangible benefits of Trump’s diplomacy.

The Hanoi summit failed to make further progress after Kim rejected Trump’s suggestion that they abandon a phased approach and “go big”, trading total North Korean nuclear disarmament for the complete lifting of sanctions. But Trump insisted the meeting had been productive and he remained on good terms with Kim.

State department spokesman Robert Palladino said on Tuesday: “Progress was made at the Hanoi summit. Yes, we did not reach an agreement. But at the same time, we were able to exchange very detailed positions, and that has narrowed the gap on a number of issues.”

The state department did not comment on the emergence of the satellite photos of Sohae, a few hours later.

The US special envoy on North Korea, Stephen Biegun, is due to hold talks in Washington on Wednesday with his South Korean and Japanese counterparts on how to revive the negotiations with North Korea after the collapse of the Hanoi summit.

Mike Pompeo, US secretary of state, said on Monday he was hopeful of sending a delegation to North Korea in the coming weeks but that he had had “no commitment yet”.

While North Korea’s official media said last week Kim and Trump had decided at the summit to continue talks, its vice foreign minister Choe Son-hui told reporters Kim “might lose his willingness to pursue a deal” and questioned the need to continue.