"We've given the United States quite a lot of time and we're waiting for an answer by the end of this year, of some kind of result... But I must say that the window of opportunity closes every day," the head of the North Korean foreign ministry's North American department said.
U.S. President Donald Trump and North Korean leader Kim Jong Un agreed in June to reopen denuclearisation talks that stalled after a failed summit in Vietnam in February. North Korean and U.S. officials met for the first time since that decision in Stockholm last month.