US envoy calls for strong message to North Korea on Flotilla attack

The world must send a strong message to North Korea that its provocative actions are unacceptable, a senior US diplomat said on Thursday after talks on how to respond to the sinking of a South Korean warship.

South Korea wants the UN Security Council to rebuke the North in a resolution imposing tough sanctions over the sinking of its navy corvette Cheonan in March, killing 46 sailors.

Pyongyang has threatened military action if it is punished for what it says is a fabricated accusation that it attacked and sank the Cheonan.

Assistant US secretary of state Kurt Campbell told reporters Washington and Seoul were trying to work closely with China, a veto-wielding permanent member of the Security Council. China is also North Korea's main ally and benefactor and has trodden a cautious line on the incident.

"We feel very strongly that the international community must take a strong stance in the face of this provocation," Campbell said after meeting South Korean officials.

"We've been very clear about sending a strong message of vigilance ... of how unacceptable this sort of provocation, this undermining of the armistice is," he said.

Campbell met South Korea's foreign minister Yu Myung-hwan and senior officials to coordinate a response by the Security Council, which has expressed grave concern about the sinking.

Neither Campbell nor South Korea's deputy foreign minister Lee Yong-joon could say whether there had been any indication from China it was showing a greater willingness to join in any UN action, but said Beijing understood what was needed.

"I think it would be fair to say China understands the gravity of the situation and currently South Korea and the United States are making very best efforts to ensure that we are working closely with China on the way ahead," Campbell said.

Analysts say neither North nor South Korea is ready to go to war but see a possibility of more skirmishes in disputed waters off the west coast or along their heavily armed land border.

Pyongyang has said the accusations against it were a US-led conspiracy aimed at giving South Korean president Lee Myung-bak a political boost.

Lee has demanded an apology from the North. The South has also cut off all trade and most humanitarian aid to its destitute neighbour, and said any aggression by the North's 1.2 million-strong army -- one of the world's largest -- would be met with swift and intense retaliation.

A team of international investigators, led by South Korea's military, said in May that a North Korean submarine torpedoed the ship, presenting evidence that included parts of the weapon recovered from the site of the incident.