Jung Pak, the State Department senior official handling North Korea, said the United States was taking no chances and would work to bolster deterrence with allies Japan and South Korea -- but saw no recent notable shift.

"Fundamentally, I don't think Kim's posture has changed," she said of North Korean leader Kim Jong Un. "I don't see an imminent or direct attack at this point."

"I'll also say that it's clear that Kim has decided that now's not the time that they want to be having dialogue and diplomacy, especially not with the United States, but clearly they're doing that with Russia," she told reporters.

So far this year, Kim has declared South Korea his country's "principal enemy," jettisoned agencies dedicated to reunification and outreach, and threatened war over "even 0.001 mm" of territorial infringement.

Pyongyang has also ramped up weapons tests, including for cruise missiles, an "underwater nuclear weapon system" and a solid-fueled hypersonic ballistic missile.

In a recent essay on the 38 North blog, scholars Siegfried Heckler and Robert Carlin said that Kim's actions show that he may have convinced himself that engagement has failed with the United States and that he must seek a military solution.

Kim met three times with Biden's predecessor Donald Trump, reducing tensions but leading to no lasting agreement.

He has rebuffed offers of renewed but lower-level dialogue with the Biden administration.

Pak reiterated that the United States was willing to talk "without preconditions" but ruled out official acceptance of North Korea's nuclear program, seen as a major goal for Kim as he seeks to preserve his totalitarian dynasty.

Recognizing North Korea as a nuclear weapons power would be "an affront to the global non-proliferation regime" and is "not on the table at all," she said.