US Secretary of State Mike Pompeo says North Korea continues work on its weapons programs despite its leader Kim Jong-un's promise to denuclearize.
Pompeo on Friday flew back to Singapore where Kim and US President Donald Trump met less than two months ago and announced a broad statement on working towards denuclearization.
Pompeo visited Pyongyang from July 5-7 for inclusive talks aimed at agreeing a denuclearization roadmap, but North Korea accused his delegation of making "gangster-like" demands.
Last month, he told the US Senate that North Korea was continuing to make bomb fuel after American media reports said Pyongyang was building new missiles.
Asked about his statement to Senate, Pompeo said, "Chairman Kim made a commitment to denuclearize. The world demanded that they (North Korea) do so in the UN Security Council resolutions."
"To the extent they are behaving in a manner inconsistent with that, they are a) in violation of one or both the UN Security Council resolutions and b) we can see we still have a ways to go to achieve the ultimate outcome we’re looking for."
A senior US official said on Monday spy satellites had detected renewed activity at the North Korean factory that produced the country’s first intercontinental ballistic missiles capable of reaching the United States.
The Washington Post claimed on Monday that North Korea appeared to be building one or two new liquid-fueled intercontinental ballistic missiles at the research facility.
North Korean Foreign Minister Ri Yong Ho is also in Singapore and will attend the same regional meeting as Pompeo on Saturday, but the State Department has not said whether the two will meet.
Following his talks with Ri, China's top diplomat, State Councillor Wang Yi, said he hoped North Korea and the United States will continue to move forward to implement their promises.
"China all along has believed that the consensus reached by US and North Korea's leaders meeting in Singapore is very precious," Wang told reporters.
"That is, at the same time as realizing denuclearization of the Korean peninsula, to establish a peace mechanism. This direction is without a doubt correct," he said.
China is North Korea's most important economic and diplomatic supporter and fought for the North in the 1950-53 Korean War against the US-led United Nations forces that backed South Korea.