While military action against Iran is a last resort, the U.S. has the resources to attack if needed despite the strains of wars in Iraq and Afghanistan, the top U.S. military officer said Thursday.

Navy Adm. Michael Mullen, the chairman of the Joint Chiefs of Staff, said the focus now is on diplomacy to stem Iran's nuclear ambitions and its support for insurgents in Iraq.

But, he told reporters, "there is more than enough reserve to respond (militarily) if that, in fact, is what the national leadership wanted to do."

Defense Secretary Robert Gates said Iran's acquisition of nuclear weapons could set of an arms race in the Middle East. "The risk of an accident or a miscalculation or of those weapons or materials falling into the hands of terrorists seem to me to be substantially increased," he said.

Appearing together before reporters for the first time since Mullen became chairman on Oct. 1, they expressed concern about Iran and Turkey — hot spots commanding attention even as the military focuses on the fighting in Iraq and Afghanistan.

Both leaders warned of serious repercussions if Congress were to pass a nonbinding resolution labeling as genocide the killing of up to 1.5 million Armenians in the final years of the Ottoman Empire, around World War I.

"I don't think the Turks are bluffing. I think it is that meaningful to them," Gates said. "I think there is a very real risk of perhaps not shutting us down" in terms of access to Turkish airspace for resupplying U.S. troops in Iraq, but of at least restricting it.

"I will say again it has potential to do real harm to our troops in Iraq and would strain — perhaps beyond repair — our relationship with a key ally in a vital region and in the wider war on terror," the Pentagon chief said.

At the same time, Gates said the U.S. and the Iraqis are "prepared to do the appropriate thing" in acting against the rebel Kurdistan Workers' Party, or PKK, that has conducted raids into Turkey from northern Iraq.

The Turks have expressed frustration about the lack of action by the U.S. against the group. Gates attributed that largely to a lack of specific intelligence.

The Turkish parliament this week authorized the government to send troops across the border to go after the Kurdish rebels, despite repeated pleas from Washington to focus on diplomatic efforts.

Gates also said he believes that Russian President Vladimir Putin is serious about trying to play a constructive role in resolving the crisis over Iran's nuclear program.

"President Putin takes Iran seriously as a security concern for Russia, and I think they are prepared to take some actions as befits that," Gates said.

Mullen said the U.S. military is working hard to stem the flow from Iran into Afghanistan of high-tech materials for roadside bombs. The military has said that parts from the armor-piercing bombs, which have killed hundreds of troops in Iraq, are now getting into Afghanistan.

Mullen said he is not aware of any high-level Iranian government connection to the weapons in Afghanistan, although officials have said that is a concern in Iraq.

At a separate Pentagon news conference, Afghanistan's defense chief, Abdul Rahim Wardak, told reporters that his government recently obtained evidence that Iranian weapons are entering his country.

He said he raised the matter with Iranian officials last month and they denied any involvement.

Also Thursday, Gates said the private security guards in Iraq — such as those who killed a number of Iraqi citizens — may be hurting the U.S. military's effort to stabilize the country.

The military and the contractors, he said, have conflicting missions. While the contractors are trying to keep alive those people being guarded, the military is striving to improve relations with the Iraqis and solidify the government.

"There have been instances where, to put it mildly, the Iraqis have been offended and not treated properly" by the private guards, Gates said. "So those kinds of activities work at cross-purposes to our larger mission in Iraq."

Gates said he plans to confer with Secretary of State Condoleezza Rice about tighter controls over the contractors.