Baghdad, Iraq (CNN) -- Iraqi leaders need to crack down on armed factions that have been targeting American troops with Iranian-supplied weapons, Defense Secretary Leon Panetta said Sunday.
The remaining U.S. force of 46,000 has come under increasing attack in recent weeks, with 14 killed by hostile fire in June and three more in the first 10 days of July. The latest was reported shortly after Panetta arrived in Baghdad from Afghanistan, the scene of the other U.S. war in the region.
Panetta said those attacks are a threat "not only to our forces, but to theirs as well."
"If we are going to be partners, they have a responsibility to protect against that kind of attack occurring," he told reporters before leaving Kabul. "It's in the interest of Iraq to provide for their own security."
The strikes have increased as Iraqi leaders debate whether to request an extension of the American presence beyond the end of 2011, when the U.S. contingent is scheduled to withdraw. Adm. Mike Mullen, the chairman of the Joint Chiefs of Staff, said last week that Iran has stepped up supplies of weapons to anti-American Shiite groups, possibly in order to claim credit for the scheduled pullout.
And radical anti-American Shiite cleric Muqtada al-Sadr, whose followers once fought pitched battles with U.S. and Iraqi government troops, has threatened to return to "armed resistance" against U.S. forces if the Americans remain.
He clarified that threat Sunday, announcing in a statement posted online that he would not reactivate his former militia, the Medhi Army. Instead, a faction known as the Promised Day Brigade would be allowed to attack only American troops, he said.
Al-Sadr's followers now control a bloc of 39 seats in Iraq's parliament. He said people claiming to be Mehdi Army members had been committing crimes in the movement's name since he first issued his threat in April.
Panetta said Washington would "certainly consider" any request from Iraq to keep U.S. forces there beyond 2011. In the meantime, he said, "We have the authority to do whatever is necessary to protect our forces, and we will do that."
He also said he would also discuss U.S. concerns about the state of Iraq's government, formed only after al-Sadr's allies broke a months-long deadlock following 2010 elections. Political disputes have prevented Prime Minister Nuri al-Maliki from naming permanent defense, interior and national security ministers, leaving him holding all three posts on an interim basis.
The United States invaded Iraq in 2003, arguing that then-Iraqi strongman Saddam Hussein was secretly harboring forbidden stockpiles of weapons of mass destruction that he could have provided to terrorists. Iraq was later found to have dismantled those weapons programs under U.N. supervision in the 1990s, though it had tried to conceal some weapons-related research from inspectors.
A bloody insurgency against U.S. and allied forces followed the invasion, with the country erupting into a spasm of sectarian warfare between its Sunni minority and Shiite majority in 2006. Nearly 4,500 Americans and 300-plus allied troops died in Iraq, while the Iraqi toll has been estimated at more than 100,000.
Much of the violence subsided after a counterinsurgency campaign launched in 2007, which brought the U.S. force to a peak of about 170,000.
CNN's Mohammed Tawfeeq contributed to this report.