The United States urged North Korea on Tuesday to tone down its bellicose rhetoric after Pyongyang's top diplomat threatened the communist nation is ready to launch a preemptive nuclear strike against the U.S.

Foreign Minister Ri Su-yong made the threat in an interview with Russia's Itar-Tass news agency published on Monday, saying the country "placed its army into the state of its readiness to deliver a preemptive nuclear strike in response to the U.S. hostile activities."

It was the latest in a series of belligerent threats and provocative acts that Pyongyang has been engaged in in recent weeks in response to a new package of U.N. Security Council sanctions and joint military exercises between South Korea and the U.S.

"We've been carefully watching what's been coming out of North Korea over the last few weeks. We've seen both the rhetoric and the provocative sanctions from the North Koreans and it continues to be a cause for concern for us," Pentagon press secretary Peter Cook said of the North's latest threat.

"We just would again urge the North Koreans to try and take the level of rhetoric down and to deescalate the situation on the Korean Peninsula. We do not think it's conducive for anyone and we continue to stand steadfastly with South Korea, with Japan and other allies in the region," he said.

Along with such war rhetoric, the North has also made a series of claims of breakthroughs in its missile and nuclear weapons programs, claiming it has succeeded in miniaturizing nuclear warheads, mastering missile reentry technology and solid-fuel rocket engine development.

The U.S. has played down such claims, saying the North has not demonstrated such capabilities. (Yonhap)