Pompeo had been scheduled to meet with top North Korean official Kim Yong Chol in New York on Thursday to push for progress on denuclearization of the Korean peninsula, but the meeting was cancelled.

"North Korea said they needed to postpone it," Haley told reporters at UN headquarters, adding: "I don't think there was some sort of major issue."

"They postponed it because they weren't ready."

"We continue to stand ready to talk," she added.

The sudden postponement came only two days after the US State Department announced the talks in New York that were also to agree on plans for a second summit between President Donald Trump and leader Kim Jong Un.

Haley said she expected the talks to be rescheduled and that plans for the second summit were on track.

Trump and Kim held a historic summit in June in Singapore -- the first ever between the two countries -- where they signed a vaguely worded deal on denuclearization.

Little progress has been made since then, with the two countries sparring over the exact meaning of the agreement.