New satellite images of North Korea suggest it is restoring a rocket launch site it had pledged to dismantle, say analysts.
The images were taken two days after talks between the leaders of the US and North Korea ended without them reaching a deal on denuclearisation.
The Tongchang-ri site has been used for satellite launches and engine testing, never for ballistic missile launches.
Work to dismantle it began last year but stopped as the US talks stalled.
The pledge to dismantle it had been seen as a confidence-building measure between Pyongyang and Washington.
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.
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.
“This distinction is important,” Jenny Town, managing editor of monitoring group 38 North, told the BBC.
“The North Koreans likely see the rebuilding not as an active part of their missile program, but of their civilian space programme – a distinction they have made repeatedly in the past.
“One would assume, the rebuilding of these structures signals a diminished lack of trust in the process,” said Ms Town.
Threats of more sanctions
The second summit between US President Donald Trump and North Korean leader Kim Jong-un ended last week in Hanoi without any deal or agreement.
The two leaders were unable to agree on how far North Korea should progress with denuclearisation before it was granted some sanctions relief.
In a television interview on Tuesday, US National Security Adviser John Bolton said North Korea could yet face more sanctions.
He said Washington would continue to watch whether Pyongyang was committed to giving up its nuclear weapons programme “and everything associated with it”.
“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.”
Observers, though, warn that adding fresh sanctions could completely stall the peace efforts.
“North Korea always reacts to the imposition of more sanctions in the same way: defiantly,” Ms Town said.
“Imposing new sanctions now is only going to deflate whatever political will there may be to keep negotiating.”