Asked if the United States would make a new attempt at the Security Council if North Korea goes ahead with a feared nuclear test, US Ambassador Linda Thomas-Greenfield said: "Absolutely we will."

"First of all we need to enforce the sanctions that we have already authority to enforce," she told reporters.

"And we certainly, as we attempted in this last resolution, will push for additional sanctions," she said.

US intelligence has said that North Korea appears to be preparing its first nuclear test since 2017, although it did not go ahead during a visit to the region earlier in May by President Joe Biden.

The United States on Thursday forced a vote at the Security Council on toughening sanctions after North Korea carried out a series of rocket launches including, according to US and South Korean officials, of an intercontinental ballistic missile.

The United States said the test was a brazen violation of a unanimous UN resolution in 2017 that warned of further consequences for tests of long-range missiles or nuclear weapons.

But China, North Korea's main ally, and Russia, whose relations with the West have deteriorated sharply over its Ukraine invasion, both vetoed the resolution, saying that new sanctions would be counterproductive and raise tensions.

The United States instead on Friday imposed new unilateral sanctions, including on two Russian banks accused of assisting North Korea on its weapons programs.

The Biden administration has said it is ready for dialogue with North Korea without preconditions.

But it has found little interest in low-level negotiations from Pyongyang, where leader Kim Jong Un held three meetings with Biden's predecessor Donald Trump that lowered tensions but failed to produce a lasting agreement.