U.S. officials are closely “monitoring” the aftermath of the latest North Korean missile test after the rogue regime claimed that its newest rocket was capable of carrying a nuclear warhead – and that its arsenal could reach American shores.

One day after Kim Jong Un’s dictatorship reported a successful test flight of its KN-17 missile, state-run news agency KCNA reported the “U.S. mainland and Pacific operations” were in range of North Korean weapons. The agency also claimed its missile was meant to verify the specifications of a new ballistic rocket “capable of carrying a large-size heavy nuclear warhead.”

“We are monitoring,” a National Security Council spokeswoman told Fox News.

HALEY: US WILL 'TIGHTEN THE SCREWS' ON NORTH KOREA

The U.S. has long been skeptical that Pyongyang has the technology to mount a nuclear warhead.

A senior administration official said the White House was warily assessing the latest news out of North Korea, given the country’s propensity to push misleading and exaggerated propaganda; however, the official said if the latest claim is true, it “would be a cause for great concern.”

Underscoring the gravity of the situation, one U.S. official told Fox News that Pyongyang took a “step forward” with its Sunday launch.

The missile flew four minutes longer than any previous ballistic missile test in the history of the communist regime, U.S. officials told Fox News, though North Korea had conducted space launches in the past that have flown longer than KN-17 – including a mission in February 2016 that sent a satellite into orbit on Super Bowl Sunday.

After three failures last month, Sunday’s liftoff was the first successful test of the liquid-fueled KN-17, which some experts see as North Korea’s best chance to develop a reliable intercontinental ballistic missile.

Aerospace expert John Schilling told Reuters the test “represents a level of performance never before seen from a North Korean missile.”

“It appears to have not only demonstrated an intermediate-range ballistic missile that might enable them to reliably strike the U.S. base at Guam,” Schilling said, “but more important, may represent a substantial advance to developing an intercontinental ballistic missile.”

U.S. Ambassador to the United Nations Nikki Haley warned Sunday that the international community will “continue to tighten the screws” around the North Korean regime. She told ABC’s “This Week” that Kim is “in a state of paranoia.”

Meanwhile, U.S. officials are looking at taking precautions. Sen. Dan Sullivan, R-Alaska, is planning to introduce a measure this week to add another 28 ground-based interceptors in Alaska and California and authorize additional missile-defense testing, Fox News is told.

Fox News’ John Roberts, Lucas Tomlinson and Serafin Gomez contributed to this report.