The United States, South Korea and Japan on Monday all urged China to help rein in its ally North Korea and vowed solidarity in defending Seoul from any further attacks from the North.

However, US Secretary of State Hillary Clinton and her counterparts Kim Sung-Hwan of South Korea and Seiji Maehara of Japan, who met in Washington were vague about how they would deal with North Korea's "belligerent" behavior.

The three-way meeting comes after North Korea shelled a South Korean border island on November 23, killing two marines and two civilians, and after it revealed a uranium enrichment program that alarmed US scientists.

Kim, the South Korean foreign minister who spoke through an interpreter, said the three shared the view that the Stalinist state in Pyongyang would face "severe consequences" if it engages in further provocations.

But it was not clear what the consequences might be.

"We all agree that North Korea's provocative and belligerent behavior jeopardizes peace and stability in Asia," Clinton said at a closing press conference with Kim and Maehara.

"We want the people of South Korea to know that we are standing shoulder-to-shoulder with you, and we are deeply committed to your defense," the chief US diplomat said.

Clinton opened the talks with a moment of silence for the dead and injured in what she described as an "unprovoked attack" on Yeonpyeong island.

She said the three top diplomats agreed that the attack violated the 1953 armistice, while the uranium enrichment program violates UN Security Council resolutions as well as its own commitment in 2005 to denuclearize.

The secretary of state nonetheless kept the door open to dialogue with North Korea.

But she said the three agreed that the North must first repair ties with the South and "cease its provocative behavior" for long-stalled six-party negotiations to resume.

The three reinforced their decision to ignore China's invitation for them and Russia to hold emergency six-party talks in Beijing this month after North Korea shelled the island.

"We appreciate Beijing's initiative to propose an emergency six-party gathering. However, we first need an appropriate basis for the resumption of talks," she said.

"Any effort, of course, must start with North Korea ceasing all provocative and belligerent behavior," she said.

The three all said they would pursue cooperation with China and Russia -- which along with North Korea are the remaining members of the six-party talks -- but stressed that China should use its leverage with its ally in Pyongyang.

"We would like China to have a more clear stance in giving warning to North Korea and to contain these provocative actions by North Korea," Kim said.

He said South Korea would consult further on this topic with Washington and Tokyo.

"We would hope that China, which chairs the six party talks, (...would) play an even greater role in relation to North Korea," Maehara said through an interpreter.

The White House said Obama, in a phone call late Sunday, urged his Chinese counterpart Hu Jintao to send "a clear message" to North Korea that its shelling of South Korean territory and other provocations were "unacceptable."

In the latest US military show of support for South Korea, the Pentagon announced it was sending its top military officer, Admiral Mike Mullen, to visit Seoul on Tuesday and Wednesday.

Officials said Mullen, the chairman of the Joint Chiefs of Staff, will meet South Korean counterparts including new Defense Minister Kim Kwan-Jin, who replaced Kim Tae-Young when the latter resigned after the shelling.

South Korea's military began a major live-fire exercise Monday, following a major show of naval strength last week by Seoul and its close ally Washington, designed to deter Pyongyang from future attacks.

The United States still has 28,000 troops deployed in South Korea, which since the 1950-53 Korean war has been divided from the North by the most heavily fortified frontier in the world.

Meanwhile, US and Japanese forces continued their biggest-ever joint military exercises, which were nonetheless scheduled before the shelling of the island.

The Washington Post meanwhile reported that the Obama administration, in an apparent toughening of its approach toward China, has privately started accusing Beijing of "enabling" North Korea to start a uranium enrichment program and to launch attacks on South Korea.

Citing an unnamed senior US official, the newspaper said Washington is moving to redefine its relationship with South Korea and Japan, potentially creating an anti-China bloc in northeast Asia.