Speaking at a news conference in Japan, US Defense Secretary Robert Gates said there was a "common interest" between the US, China, South Korea and Japan in securing peace and stability on the Korean peninsula.
And he stressed that it is time for North Korea to get "serious" about negotiations for peace. "There must be concrete evidence that they are finally serious about negotiations," Mr Gates said of the leadership in Pyongyang.
North Korea has offered talks, and the reopening of tourism and industrial projects in recent days, but South Korea, the US and Japan have responded skeptically.
Speaking in Washington, US Joint Chiefs of Staff Chairman Mike Mullen said North Korea posed "an evolving threat, not just to the region but to the United States specifically".
Mr Gates was in China for 4 days, is presently in Japan and heads to South Korea on Friday.