National Security Council spokesman John Kirby speaks during the daily briefing at the White House in Washington, Oct. 26. AP-Yonhap

The United States remains concerned about a potential North Korean nuclear test, a National Security Council (NSC) spokesperson said Tuesday, reiterating Pyongyang may conduct a nuclear test "at any time."

John Kirby, however, noted it was not clear when exactly North Korean leader Kim Jong-un might conduct a test.

"We have said for a long time that they could conduct a nuclear test at anytime, and it's difficult to predict with any degree of certainty what the triggering event might be for Kim Jong-un to conduct any number of provocations that he has in recent weeks or he might in future weeks," the NSC strategic communications coordinator said when asked if the North may conduct a nuclear test during the Group of 20 summit, slated to be held in Bali, Indonesia on Nov. 15-16.

North Korea fired more than a dozen ballistic missiles since late September.

"So I would say, in general, our concern remains high and consistently so about the potential for a nuclear test," Kirby added in a telephonic press briefing.

Seoul officials have said the North will likely conduct a nuclear test before the U.S. midterm elections to be held next Tuesday. (Yonhap)