U.S. Defense Secretary Robert Gates says there must be concrete evidence that North Korea is finally serious about negotiations.

Gates made the remark during a joint news conference that was held on Thursday after he met with Japanese Defense Minister Toshimi Kitazawa in Tokyo.

Gates said that he hopes Japan will play an increased role in maintaining the security situation on the Korean Peninsula and in the Northeast Asian region as a whole.

Gates, in regards to South Korea’s vow to exercise its right of self-defense in the face of North Korean provocations, added that "it's a long-standing principle that every country has the right to protect itself and defend itself against an unprovoked attack."

Meanwhile, Kitazawa denounced recent North Korean provocations and emphasized Japan’s full support for South Korea.