North Korean leader Kim Jong-Un celebrating the successful test-fire of the intercontinental ballistic missile Hwasong-14 at an undisclosed location.

North Korea appears to be building one or two new liquid-fueled intercontinental ballistic missiles at a factory that produced the country's first missiles capable of reaching the United States, the Washington Post reported on Monday.

The newspaper, citing unidentified officials familiar with intelligence reporting, said U.S. spy agencies were seeing signs of the construction at a large research facility in Sanumdong, on the outskirts of Pyongyang.

The findings are the latest to suggest ongoing activity in North Korea's nuclear and missile facilities despite arms talks with the United States and a recent summit between North Korean leader Kim Jong Un and U.S. President Donald Trump.

U.S. Secretary of State Mike Pompeo told the U.S. Senate Foreign Relations Committee last week that North Korea was continuing to produce fuel for nuclear bombs despite its pledge to denuclearize. But he insisted the Trump administration was still making progress in its talks with Pyongyang.

Trump said in a Twitter post after his historic summit with Kim in Singapore last month: "Everybody can now feel much safer than the day I took office. There is no longer a Nuclear Threat from North Korea."

Kim committed in a broad summit statement to work toward denuclearization, but Pyongyang has offered no details as to how it might go about that.