North Korea appears to have begun dismantling part of a key rocket launch site in the country's north-west.
US President Donald Trump said North Korea's leader Kim Jong-un had vowed to destroy an engine test site, but did 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 and Kim Jong-un in Singapore last month, the two leaders signed a deal to work towards the "complete denuclearization of the Korean Peninsula".
But the deal was criticised for a lack of details on when or how Pyongyang would renounce its nuclear weapons.
Earlier on Monday, 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.
North Korea has carried out a total of six nuclear tests, the most recent of which took place in September last year.
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