"I do not think the regime in Pyongyang wants to commit suicide, but that, as they must surely know, would be the result of any attack on the United States," Senator Bob Menendez told the Senate Foreign Relations Committee.

He was speaking as the United Nations adopted tough new sanctions on North Korea for last month's nuclear test, and as Pyongyang said a new war was "unavoidable" on the peninsula because of South Korean-US military exercises.

The North's military "will exercise the right to a pre-emptive nuclear attack to destroy the strongholds of the aggressors," Pyongyang's foreign ministry said.

Menendez told Thursday's committee hearing on US policy towards North Korea that the threat was "absurd."

But he warned: "There should be no doubt about our determination, willingness, and capability to neutralize and counter any threat that North Korea may present."

North Korea has accumulated some 20 to 40 kilos of plutonium, "enough for perhaps six to eight nuclear weapons," Menendez said. It is also seeking the capability to fit a nuclear warhead to an intercontinental ballistic missile.

"In time, if its present course remains unaltered, North Korea will pose a direct threat to the United States," Menendez warned.

"Today, North Korea certainly poses a growing threat to our allies and to American forces in region."