United Nations Secretary-General Antonio Guterres said Thursday that Security Council members must unite to denuclearize North Korea, warning that the worst case scenario would be "sleepwalking" into war.

"The unity of the Security Council is crucial" to allow possible "diplomatic engagement that allows denuclearization to take place in a peaceful way," Guterres told a group of reporters soon after a meeting in Tokyo with Prime Minister Shinzo Abe.

The meeting came after U.S. Secretary of State Rex Tillerson said Tuesday that Washington was ready to have direct talks with North Korea without preconditions. But on Wednesday the White House distanced itself from that idea, announcing that North Korea must first improve its behavior in order for negotiations to take place.