North Korea appears to have begun dismantling part of a key rocket launch site in the country's north-west.
Satellite images of the Sohae station seen by US-based monitoring group 38 North suggest Pyongyang is complying with a promise made to the US in June.
US President Donald Trump said North Korea's leader Kim Jong-un had vowed to destroy an engine test site, but did not specify which one.
Pyongyang has maintained that Sohae is a satellite launch site.
But US officials suspect that it has been used to test ballistic missiles.
During a landmark meeting between President Donald Trump and Kim Jong-un in Singapore last month, the two leaders signed a deal to work towards the "complete denuclearisation of the Korean Peninsula".
But the deal was criticised for a lack of details on when or how Pyongyang would renounce its nuclear weapons.
The apparent dismantling of the Sohae test site comes amid rising questions over North Korea's willingness to stick to the pledges made at the 12 June summit.
Earlier on Monday, President Trump said that he was "very happy" with the progress in relations with North Korea, saying that Pyongyang had not launched any missiles or carried out any nuclear tests during the last nine months