U.S. National Security Advisor Jake Sullivan speaks to the media about the war in Ukraine and other topics at the White House in Washington, U.S., March 22. Reuters-Yonhap

North Korea is currently in a provocation cycle that may last for weeks or even months, U.S. National Security Advisor Jake Sullivan said Thursday.

Sullivan also said the North will continue efforts to advance its nuclear weapons and missile programs, but that the capability to hit the U.S. mainland has yet to be proven.

"A few weeks ago, they tested an intercontinental ballistic missile, which they had not done previously, they had not done since 2017. So yes, they are in a pattern of provocation, pattern of testing," Sullivan said in a seminar hosted by the Economic Club of Washington D.C., a non-profit organization based in Washington.

"I think you will hear more out of North Korea in terms of its efforts to advance its nuclear program and its missile program in the weeks and months ahead," he added.

The remarks come as North Korea celebrates the anniversary of the birth of late founding leader Kim Il-sung, Friday (KST), an occasion that has often been marked by a show of military strength.

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"What I can say and what we know is that the DPRK in the past has used the occasion of holidays and other notable occasions within the DPRK to engage in provocations," Department of State spokesperson Ned Price said earlier, referring to North Korea by its official name, the Democratic People's Republic of Korea.

North Korea has so far conducted 12 missile launches this year, including the firing of an intercontinental ballistic missile (ICBM), March 24, that ended the North's self-imposed moratorium on long-range missile testing after over four years.

Officials in Seoul have also noted ongoing work to repair underground tunnels at North Korea's Punggye-ri nuclear test site that Pyongyang purportedly dismantled in 2018, suggesting a possible nuclear weapons test down the road. North Korea staged its sixth and last such test in September 2017.

Sullivan said the North Koreans "obviously have nuclear weapons," when asked if Pyongyang currently has a nuclear-tipped ICBM that can reach the U.S.

However, he added, "The question of whether they can mate a nuclear warhead to an intercontinental ballistic missile, fire it and actually have it hit a target as they would want to in the continental United States, that is something that is not yet proven."

The White House official said the U.S. was coordinating closely with South Korea and Japan, as well as China, on the North Korean issue.

"We are coordinating closely with both the outgoing and incoming ROK government, and with Japan. And I was just in Rome a few weeks ago with my Chinese counterpart, so we're talking to Beijing about this as well," he said, referring to South Korea by its official name, the Republic of Korea.

Sullivan met with a special delegation of South Korean President-elect Yoon Suk-yeol in Washington last week.

Yoon is set to take office May 10. (Yonhap)