U.S. Backs Seoul's Charge That North Korea Sank Ship

"Such unacceptable behavior only deepen North Korea's isolation," the White House said in a statement. It strengthens the resolve of its neighbors to step up cooperation to ensure peace and stability in the region against all provocations. "

The U.S. government echoed Seoul's claim that an international investigation had given evidence that a North Korean submarine fired the torpedo that hit the South Korean ship in March killed 46 sailors.

"The point overwhelmingly to the conclusion that North Korea was responsible for this attack," the White House said.

"This act of aggression is yet another instance of North Korea are unacceptable and contrary to international law," it said. "This attack is a challenge to international peace and security and is a violation of the ceasefire agreement."

Obama spoke by telephone with South Korean President Lee Myung-bak two days ago, the statement said, and "made it clear that the U.S. fully supports the Republic of Korea, in efforts to secure justice for the 46 members killed in the attack and in defense against further attacks. "

Obama's efforts to engage diplomatically with a nuclear North Korea in the first days of his administration last year was met with defiance, and the U.S. leader has since tempered his rhetoric against Pyongyang over its nuclear program.

Lee has promised a firm response to North Korea.

Pyongyang called the accusation a fabrication and threatened harsh measures, including war if South Korea imposed sanctions.

Seoul bid to further isolate North Korea can also lead to a US-backed push for tougher UN sanctions against North Korea that could tighten the vise on its already impoverished economy.

Beijing, a key player for a long stopping six-party talks in North Korea's nuclear weapons deer program, reclusive state only major ally and is reluctant to punish the government for fear of causing instability in the border.

North Korea has denied it was responsible for the ship sinks, accusing South Conservative government to use the incident for political gain and to aggravate the already chilly ties between the two Korea's.

U.S. Secretary of State Hillary Clinton visited Seoul on the 26th Can analysts see as a solidarity with the long time U.S. ally.