WASHINGTON, April 12 (UPI) -- Tribal leaders in southern Iraq are making advances against Iranian-supported militias in Basra, U.S. Gen. David Petraeus and Ambassador Ryan Crocker say.

The militias, loyal to anti-American cleric Moqtada Sadr "is something that has to be dealt with," said Petraeus, the top U.S. commander in Iraq, at a meeting with reporters at the Pentagon, The Washington Times reported Saturday.

"The population has turned against the militia in most areas in Basra. Interestingly, it has turned against them in a number of areas in Baghdad as well."

Crocker said he returned from a recent visit "sobered by the extent ... the militias had free rein in Basra." The U.S. ambassador to Iraq added that he received "an earful" of complaints from sheiks in southern Iraq about the militias, who are believed to be armed by Iran, a claim the government of Iranian President Mahmoud Ahmadinejad has denied.

Crocker said Iraqi Prime Minister Nouri al-Maliki "tapped into" the frustration over the militias and the Iraqis now are "standing up" to help battle the Shiite militias.