WASHINGTON -- US Secretary of State Mike Pompeo expressed confidence Wednesday that North Korea understands the scope of the US request for denuclearization.

Speaking at a Senate hearing, the top US diplomat refused to discuss details of ongoing negotiations between the countries to dismantle the regime's nuclear weapons program.

But he said he is confident the North Koreans understand "the scope of the request we're making with respect to denuclearization."

At a historic summit in Singapore earlier this month, US President Donald Trump and North Korean leader Kim Jong-un agreed to the "complete denuclearization" of the Korean Peninsula in exchange for security guarantees from the US.

Details are expected to be hashed out in follow-up negotiations led on the US side by Pompeo.

On North Korea's promise to return the remains of some American soldiers killed in the 1950-53 Korean War, Pompeo clarified that the US has yet to receive them.

Trump sowed confusion last week when he claimed that the remains had already been sent back.

Pompeo said he is "optimistic" that the US will receive the remains "in the not-too-distant future."

North Korea continues to pose a nuclear threat, he said, adding that Trump's assertion that the threat no longer exists was meant to deliver the point that "for the moment, we have reduced the risk."

And sanctions on North Korea will remain in place until denuclearization is achieved.

"It is the case that the enforcement of the existing sanctions remains an enormous priority of this administration," Pompeo said.

"I say it a dozen times a day no matter who walks into my office and what country they are from."

China has relaxed sanctions enforcement across the border from six or 12 months ago, but "they had been enforcing sanctions in a way that we have never seen them enforce them before," said Pompeo.

"The things they do today don't violate" UN Security Council sanctions against North Korea, he said. "So they are still on our side."

Pompeo was asked if diplomatic failure would remove peaceful options to denuclearize the regime.

He answered affirmatively, but added that he thinks the North Koreans "appreciate" that the US is also serious about fulfilling its side of their summit agreement.

Trump suspended joint military exercises between South Korea and the US, saying it would help conduct negotiations with North Korea in good faith.

The US troop presence in South Korea, however, remains a stabilizing force in the region, Pompeo said. (Yonhap)