The new chairman of the U.S. Joint Chiefs of Staff said in an interview published Monday that the prolonged military campaigns in Iraq and Afghanistan may have undermined the military's ability to fight wars against major adversaries - including Iran.

With the United States already heavily committed in wars in two Muslim countries, Joint Chiefs Chairman Admiral Mike Mullen told The New york Times that an offensive against Iran, a third Mideast Islamic state "has extraordinary challenges and risks associated with it." He counseled against an immediate attack on Iran, saying that the military option should be a last resort.

But Mullen warned Iran and other nations not to "mistake restraint for lack of commitment or lack of concern or lack of capability."

"Because we have had such an intense focus on the Middle East and Iraq and Afghanistan, there is risk associated with those other parts of the world," Admiral Mullen said.

Asked whether the American military should aim at sites inside Iran if intelligence indicated that such action could stem the flow of bombs into Iraq, he said "the risks could be very, very high."

"We're in a conflict in two countries out there right now," he added. "We have to be incredibly thoughtful about the potential of in fact getting into a conflict with a third country in that part of the world."

Speaking of his visits to soldiers and marines in Iraq and Afghanistan in recent weeks, Mullen said: "They're tired. They've been doing unbelievably great work for our country. And we need to make sure we take care of them and their families."

Regarding prolonged and repeated deployments for the ground forces in Iran and Afghanistan, he said, "The ground forces are not broken, but they are breakable."