North Korea will not get any sanctions relief until it has demonstrated "complete denuclearisation", US Secretary of State Mike Pompeo has said.
Mr Pompeo was speaking at a press conference in Seoul with his South Korean and Japanese counterparts.
He said Pyongyang was committed to giving up its nuclear programme.
The conference comes two days after President Donald Trump and Kim Jong-un held a historic summit in Singapore.
Mr Pompeo has travelled to South Korea to brief the US's regional allies on the agreement Mr Trump signed with the North Korean leader.
"We believe that Kim Jong-un understands the urgency [of denuclearisation]," said Mr Pompeo. "That we must do this quickly."
There has been deep scepticism about the deal the two leaders signed on 12 June, with observers saying it lacked detail on how North Korea would give up its nuclear weapons and how that process would be verified.