WASHINGTON - The Obama administration announced plans Monday for two major military exercises off the Korean peninsula in a show of force aimed at North Korea, which has been blamed by investigators for a deadly torpedo attack on a South Korean warship.

The White House called U.S. support for South Korea "unequivocal" and said in a statement that President Barack Obama had directed military commanders to work with the South "to ensure readiness and to deter future aggression." North Korean leaders have denied responsibility and warned against any retaliation, but Secretary of State Hillary Rodham Clinton blamed the North for the crisis Monday.

"We are working hard to avoid an escalation of belligerence and provocation," Clinton told reporters in Beijing, where she was to press China to support diplomatic action against its neighbor and ally, North Korea. "This is a highly precarious situation that the North Koreans have caused in the region." U.S. officials hope a united international response, coupled with a display of military might, will deter North Korea's neo-Stalinist regime from ratcheting up tensions.

Last week, an international team of investigators blamed the North for the March 26 sinking of the South Korean corvette, the Cheonan. Investigators said the ship was ripped in two by a torpedo, killing 46 sailors.

Until Monday, the Obama administration had been intentionally vague on how it might respond to the report blaming North Korea for the attack, out of a reluctance to stoke tensions.

But on Tuesday, the Obama administration shifted gears, taking its cue from South Korean President Lee Myung-bak, who announced Monday that he would cut all trade with the impoverished North.

A Defense Department spokesman, Bryan Whitman, said the joint U.S.-South Korean exercises would take place in the "near future" and would focus on detecting submarines and monitoring illicit activities.

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