The United States on Thursday warned North Korea of consequences after a investigation concluded it sank a South Korean warship, but China called for restraint amid a chorus of international outrage.

Western nations and Japan were quick to voice solidarity with South Korea after a long-awaited multinational investigation found that a North Korean submarine torpedoed the Cheonan on March 26, killing 46 sailors.

The United States, which stations 28,500 troops in South Korea under a security alliance, condemned North Korea's sinking of the warship as an "unprovoked, unwarranted" act of aggression.

"This was a serious provocation. There will be definitely be consequences," State Department spokesman Philip Crowley told reporters.

The United States did not specify its counter-measures. White House spokesman Robert Gibbs, asked repeatedly at a news briefing about the US response, said only that "a lot of things" were on the table.

In a sign the United States was not expecting tensions to abruptly escalate, the head of the US military, Admiral Mike Mullen, said US troops had not been put on a state of alert, despite Pyongyang's threats of "all-out war" in response to any effort to punish it.

"The forces are clearly aware of what's gone on, but we haven't changed any readiness levels as a result of this, up to this point," Mullen said.

Secretary of State Hillary Clinton was en route to Japan, China and South Korea for talks on a previously scheduled visit. Defense Secretary Robert Gates said the Pentagon was also in "close consultation" with South Korea.

The United States has already hinted at one consequence -- no quick resumption of six-nation talks on North Korea's nuclear disarmament.

North Korea stormed out of the talks last year before testing its second nuclear bomb, but has since been keen to negotiate with the United States.

Kim Jong-Il's regime is seeking a permanent peace treaty with the United States that would finally put an official end to the 1950-53 Korean War -- and, in effect, bestow recognition on his isolated state.

US lawmakers also united behind South Korea, with some urging a further toughening of sanctions against the North.

Republican Senator Sam Brownback called for the United States to reclassify North Korea as a state sponsor of terrorism. Former president George W. Bush removed Pyongyang -- opening the way for it to receive international loans -- as a concession during talks.

But China, the main diplomatic and economic partner of the impoverished North, was alone in stopping short of condemning Pyongyang.

"We maintain that parties involved should stay calm and exercise restraint and properly handle the issue so as to avoid the escalation of the situation," foreign ministry spokesman Ma Zhaoxu told reporters.

"We stand for safeguarding regional peace and stability, promoting the six-party talks and the denuclearization of the Korean peninsula," he said.

Beijing fears punitive measures taken against North Korea could lead to a collapse of its hardline regime and possibly millions of starving refugees on its doorstep, experts say.

Experts also see China as benefiting from the division of the Korean peninsula, which provides a buffer state separating it from the US troops in South Korea.

There was no immediate reaction from Russia, another member of the six-nation talks, which historically has enjoyed warm relations with Pyongyang.

Japan, which has long advocated a hard line against North Korea, said it fully supported South Korea.

Prime Minister Yukio Hatoyama called the torpedo attack "unforgivable" and offered for Japan to spearhead any resolution at the UN Security Council against North Korea.

The United Nations said the findings against North Korea were "deeply troubling," while Australia, Britain, France and the European Union offered condemnation.

A spokesman for the French foreign ministry called on North Korea to "abandon the path of murderous violence" and return to negotiations.

Canadian Foreign Minister Lawrence Cannon meanwhile called on Pyongyang to account for the "violent act of aggression."

Canada sent three naval experts to join the multinational investigation of the sinking, and remains "fully supportive" of South Korea, "our democratic ally and friend," Cannon said.

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