Sung Kim, the Special Representative for North Korea Policy, said Washington thinks Pyongyang could be planning a big show of its growing nuclear weapons capacity on the annual holiday next week, which will celebrate the 110th anniversary of the birth of Kim Il Sung, who founded the modern Democratic People's Republic of Korea (DPRK).

"We are worried that in connection with the upcoming April 15 anniversary, the DPRK may be tempted to take another provocative action," Kim told reporters, referring to North Korea's recent ballistic missile test launches.

"I don't want to speculate too much, but I think it could be another missile launch, it could be a nuclear test," he said.

North Korea has tested nuclear weapons several times starting in 2006, and its last test was in 2017.

Pyongyang has continued to ignore Washington's overtures to resume discussions about removing all nuclear weapons from the Korean peninsula, Kim said.

"We have not received any response from Pyongyang, which is very disappointing, because we have sent several messages, both public and private, inviting them to a dialogue without any conditions," he said.

"Instead they have initiated a series of missile tests that recently culminated in at least three ICBM launches. These actions pose a serious threat to regional stability."

Kim also said that China and Russia were not helping President Joe Biden's push to restart talks with North Korean leader Kim Jung Un.

Talks aimed at containing Pyongyang's nuclear threat appeared to gain traction under the previous US administration of Donald Trump, but then stopped.

After Biden took office, North Korea began a series of missile tests, 13 in all, that culminated last month with the test of a ballistic missile that could potentially deliver a nuclear warhead to the eastern United States.

The tests have alarmed North Korea's immediate neighbors South Korea and Japan.

On Tuesday, Kim Jong Un's powerful sister Kim Yo Jong warned that Pyongyang will use its nuclear weapons to "eliminate" South Korea's army in the event they launch a preemptive strike.

Sung Kim said that Washington is pushing for a fresh resolution condemning Pyongyang's actions at the UN Security Council.

But he noted that in six earlier efforts this year, Russia and China "have consistently blocked our efforts to produce a UN public statement."