Six-Party Talks

Washington insists that the Six-Party Talks on denuclearization is the only forum at which it will sit with Pyongyang.

While in Asia, Kerry has talked tough on the DPRK's "unacceptable" rhetoric, but also sought to lower the temperature by supporting dialogue with Pyongyang and saying he would be "prepared to reach out" to the DPRK.

In Seoul, he gave Washington's public blessing to peace overtures made by ROK's new president, Park Geun-hye, who in recent days has signaled the need to open a dialogue and "listen to what North Korea thinks".

But the DPRK rejected the overtures as "empty talk" and a "crafty trick" to conceal Seoul's aggressive intentions.

"It is very regrettable that the North dismissed our offer," the ROK Unification Ministry said on Monday, labeling Pyongyang's response "totally incomprehensible".

The DPRK's current leader and Kim Il-sung's grandson, Kim Jong-un, opened Monday's birthday events with a visit to the mausoleum in Pyongyang housing the embalmed bodies of his grandfather and his father Kim Jong-il.

ROK and US forces have been on a heightened state of alert for days, and Japan has deployed Patriot anti-missile systems around Tokyo and promised to shoot down any missile deemed to be a threat.

Following Pyongyang's repeated threats to attack the US and its allies, the US has beefed up its military presence in the Asia-Pacific region in recent weeks, deploying two missile defense systems.

During his trip in Japan, Kerry also defended the re-orientation of US foreign policy toward Asia, trying to assuage China's concerns even as he offered reassurance to US allies such as Japan and the ROK that it wasn't going anywhere.

"Some people might be skeptical of America's commitment to this region," Kerry told students at the Tokyo Institute of Technology. "My commitment to you is that as a Pacific nation that takes our Pacific partnership seriously, we will continue to build on our active and enduring presence."

China Daily—AFP—Reuters

Zhou Wa contributed to this story.