South Korea to take lead on next steps after attack: U.S.

Navy soldiers stand guard near the wreckage of the naval vessel Cheonan, which was sunk on March 26 near the maritime border with North Korea, at the Second Fleet Command's naval base in Pyeongtaek, south of Seoul, May 19, 2010.

WASHINGTON (Reuters) - South Korea will be in the lead in deciding how to respond to what it says was a North Korean torpedo attack on one of its warships, U.S. Defense Secretary Robert Gates said on Thursday.

Gates, however, rejected any suggestion that the United States was not in a position to respond militarily to North Korean aggression because it is stretched thin by wars in Iraq and Afghanistan.

"If there were a problem in Korea, our main arms would be the Navy and the Air Force and those are not stretched in the same way that the ground forces are," Gates told reporters at the Pentagon, adding the U.S. was consulting with Seoul.

"But again the key thing to remember here is that this was an attack on a South Korean ship. And the South Koreans need to be in the lead in terms of proposing ways forward."

South Korea accused the North earlier on Thursday as it announced the results of its investigation into the March sinking of the Cheonan corvehtte, which killed 46 South Korean sailors.

Seoul said it would take "firm" measures against its impoverished neighbor. North Korea responded that it was ready for war if Seoul or its allies imposed sanctions.

Gates stressed that Washington fully backed the findings of the South Korean investigation.

The top U.S. military officer said American forces in South Korea had not been placed on a heightened state of readiness, despite heightened tensions between North and South Korea. following Seoul's announcement.

"We haven't changed any readiness levels up to this point," Admiral Mike Mullen, chairman of the U.S. Joint Chiefs of Staff, told reporters.

The two Koreas, technically still at war, have more than 1 million troops near their border. The United States has about 28,000 troops in the South to support its military.

(Editing by Sandra Maler and Cynthia Osterman)