North Korea has not lived up to denuclearisation deal: White House

White House national security adviser John Bolton on Tuesday said North Korea has not taken the steps necessary to denuclearize despite an agreement made between Pyongyang's leader Kim Jong-un and US President Donald Trump in June.

Bolton, speaking in an interview on Fox News, also said US Secretary of State Mike Pompeo was prepared to return to North Korea for another meeting with Kim.

North Korea has not stopped its nuclear and missile programs in violation of United Nations sanctions, according to a confidential UN report seen by Reuters on Friday.

The six-month report by independent experts monitoring the implementation of UN sanctions was submitted to the Security Council North Korea sanctions committee late on Friday.

Earlier, US intelligence agencies believe North Korea has increased production of fuel for nuclear weapons at multiple secret sites in recent months and may try to hide these while seeking concessions in nuclear talks with the United States, NBC News quoted US officials as saying.

In a report on Friday, the network said what it described as the latest US intelligence assessment appeared to go counter to sentiments expressed by President Donald Trump, who tweeted after an unprecedented June 12 summit with North Korean leader Kim Jong Un that "there is no longer a nuclear threat from North Korea." NBC quoted five unidentified US officials as saying that in recent months North Korea had stepped up production of enriched uranium for nuclear weapons, even as it engaged in diplomacy with the United States.

The network cited US officials as saying that the intelligence assessment concludes that North Korea has more than one secret nuclear site in addition to its known nuclear fuel production facility at Yongbyon. "There is absolutely unequivocal evidence that they are trying to deceive the US," NBC quoted one official as saying. The CIA declined to comment on the NBC report. The State Department said it could not confirm it and did not comment on matters of intelligence. The White House did not respond to a request for comment.

The NBC report raises further questions about North Korea's readiness to enter serious negotiations about giving up a weapons program that now threatens the United States, in spite of Trump's enthusiastic portrayal of the summit outcome. NBC quoted one senior US intelligence official as saying that North Korea's decision ahead of the summit to suspend nuclear and missile tests was unexpected and the fact that the two sides were talking was a positive step.

However, he added: "Work is ongoing to deceive us on the number of facilities, the number of weapons, the number of missiles ... We are watching closely." Jeffrey Lewis, director of the East Asia Nonproliferation Program at California's Middlebury Institute of International Studies, said there were two "bombshells" in the NBC report. He said it had long been understood that North Korea had at least one undeclared facility to enrich nuclear fuel aside from Yongbyon.

"This assessment says there is more than one secret site. That means there are at least three, if not more sites," he said.Lewis said the report also implied that US intelligence had reporting to suggest North Korea did not intend to disclose one or more of the enrichment sites. "Together, these two things would imply that North Korea intended to disclose some sites as part of the denuclearization process, while retaining others," he said.

North Korea agreed at the summit to "work toward denuclearization of the Korean Peninsula," but the joint statement signed by Kim and Trump gave no details on how or when Pyongyang might surrender its nuclear weapons.Ahead of the summit, North Korea rejected unilaterally abandoning an arsenal it has called an essential deterrent against US aggression.