Japan Thursday demanded North Korea take "concrete actions" before renewed dialogue can resume on the divided Korean peninsula, a day after Pyongyang offered unconditional talks with the South.

"The nuclear and missile development issue of DPRK (North Korea) is a cause for major concern," Japanese Foreign Minister Seiji Maehara said in a speech in Washington before meeting with US Secretary of State Hillary Clinton.

"What is most important is that a North Korea-South Korea dialogue be opened up," Maehara told the Center for Strategic and International Studies.

But, North Korea "needs to first take concrete actions," he said, without providing further details.

North Korea offered "unconditional" negotiations with the South on Wednesday, in its most conciliatory remarks since the nuclear-armed state sent tensions soaring in November by shelling a South Korean island.

Its most important ally, Beijing, on Thursday threw its support behind the initiative by Pyongyang, locked in a standoff with the international community over its disputed nuclear program.

"We support and welcome relevant parties to have contact and dialogue, and make active interactions to jointly steer the situation in a desirable direction," Chinese foreign ministry spokesman Hong Lei told reporters.

The words of support came as the US special envoy on North Korea, Stephen Bosworth, pursued a three-nation tour across the region to sound out officials in Seoul, Beijing and Tokyo on how to proceed.

Speaking through a translator during a question-and-answer session, Maehara said North Korea "these days is escalating the level of its provocation against the region and the international community."

He referred to the sinking of a South Korean warship last May, as well as the North's deadly shelling of a South Korean border island in November that sparked some of the worst saber-rattling since the 1950-1953 war.

He also cited a long-running dispute with Pyongyang over Japanese citizens abducted by North Korean spies in the 1970s and 80s. The kidnap victims were forced to train Pyongyang's secret agents in Japanese language and culture.

China has also called for a meeting of the six powers involved in the suspended negotiations over North Korea's nuclear disarmament. They are the two Koreas, China, the United States, Japan and Russia.

"There will be no reason for us to reject that" Chinese call, if North Korea takes concrete actions to reduce tension and end provocations, Maehara said during a press conference with Clinton.

"We are determined to move forward to end the provocative behavior and to once again focus on the denuclearization of the Korean peninsula," Clinton added.

Earlier this week, Maehara said Japan was open to direct talks with North Korea this year, following conciliatory New Year's statements out of Seoul and Pyongyang.

Washington also welcomed the change in tone, but has insisted that North Korea match its words with deeds while calling on China to rein in its ally.

The Japanese envoy's visit to Washington comes less than two weeks before a visit by Chinese President Hu Jintao in which North Korea will figure high on the agenda.

In an unusually cordial statement, carried by the state KCNA news agency, North Korea on Wednesday said it "courteously proposes having wide-ranging dialogue and negotiations."

Pyongyang is "ready to meet anyone, anytime, anywhere", it said, calling for "unconditional and early opening of talks" with officials with "real power and responsibility."

South Korea dismissed the approach.

"We don't consider it as a serious offer for dialogue," unification ministry spokeswoman Lee Jong-Joo told AFP.

The North has previously refused to discuss the nuclear issue directly with the South, saying it wants to deal only with Washington, but its latest statement suggested it may be willing to engage with Seoul on the topic.

North Korea sharply heightened tensions in November when it launched the artillery strike that killed four people in the South and unveiled a uranium enrichment plant that experts fear could help it make atom bombs.

Meanwhile, UN chief Ban Ki-moon met Thursday with Chinese Foreign Minister Yang Jiechi at the UN headquarters in New York and the two men stressed the need to soon resume the six-party talks, a UN spokesman said.

Yang visited UN headquarters as part of a US tour to lay the ground for Hu's upcoming visit.