Secretary of State John Kerry said Monday the US will talk with North Korea if it takes "meaningful steps" towards peace, as the world watched to see if Pyongyang will mark its founder's birthday with a missile launch.

The isolated state has a habit of linking high-profile military tests with key dates in its annual calendar and expectations are high that it could fire two medium-range missiles in honour of late former leader Kim Il-Sung.

But Kerry, speaking in Japan on the last leg of an Asian tour dominated by the crisis on the Korean peninsula, appealed to the North to step back.

"The United States remains open to authentic and credible negotiations on denuclearisation, but the burden is on Pyongyang," he said.

"North Korea must take meaningful steps to show it will honour commitments it has already made."

Kerry, whose three-country tour wraps up in Tokyo on Monday after a meeting with Prime Minister Shinzo Abe, said talks in China and in South Korea had already demonstrated the world was speaking with one voice.

"One thing is certain: we are united. There can be no confusion on this point," he said.

"The North's dangerous nuclear missile program threatens not only North Korea's neighbors, but also its own people."

The Korean peninsula has been in a state of heightened military tension since the North carried out its third nuclear test in February.

Incensed by fresh UN sanctions and joint South Korea-US military exercises, Pyongyang has spent weeks issuing blistering threats of missile strikes and nuclear war.

Washington insists that the "six-party" talks on denuclearisation -- which take in both Koreas, Japan, Russia, China and the US -- is the only forum at which it will sit with Pyongyang.

While in Asia, Kerry has talked tough on the North'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 North Korea.

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

Park had campaigned on a promise of greater engagement with Pyongyang, but had her hands tied by the international outcry over the North's nuclear test and the subsequent sharp escalation of tensions.

The North's immediate response to her latest remarks was negative, with a spokesman for the North's Committee for the Peaceful Reunification of Korea suggesting the dialogue overtures were a "cunning" ploy.

"We found the offer an empty, meaningless act," the spokesman said in an interview Sunday with the state media KCNA.

"If the South is genuine about having talks... it should first abandon its confrontational posture," he said, citing ongoing military drills with the US.

North Korea's current leader and Kim Il-Sung's grandson, Kim Jong-Un, opened Monday's anniversary events with a visit to the mausoleum housing the embalmed bodies of both his grandfather and his father Kim Jong-Il.

State television interspersed musical programming with documentaries on the life of Kim Il-Sung and footage of Korean soldiers honing their martial arts skills.

The missiles mobilised by the North are reported to be untested Musudan models with an estimated range of up to 2,485 miles (4,000 kilometres).

That would cover any target in South Korea and Japan, and possibly even US military bases on the Pacific island of Guam.

South Korean 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.

In Beijing on Saturday, Kerry pressed Chinese leaders to take a firmer stand with North Korea.

China is Pyongyang's sole major ally and backer, and is widely seen as the only country with leverage to influence its actions -- although it is reluctant to risk destabilising the regime.

Kerry won a promise that China would work together with the United States to reduce tensions and persuade the North to give up its nuclear weapons programme.

The ball now lies in Pyongyang's court in terms of pushing ahead with a missile launch or not, and observers note that the North's response to diplomatic pressure in the past has often been a provocative show of force.