Baghdad ? Rescuers used bare hands and shovels Wednesday to claw through clay houses shattered by an onslaught of suicide bombings that killed at least 250 and possibly as many as 500 members of an ancient religious sect in the deadliest attack of the Iraq war.

The U.S. military blamed al-Qaida in Iraq, and an American commander called the assault an “act of ethnic cleansing.”

The victims of Tuesday night’s coordinated attack by four suicide bombers were Yazidis, a small Kurdish-speaking sect that has been targeted by Muslim extremists who consider its members to be blasphemers.

The blasts in two villages near the Syrian border crumbled buildings, trapping entire families beneath mud bricks and other wreckage. Entire neighborhoods were flattened.

“This is an act of ethnic cleansing, if you will, almost genocide,” Army Maj. Gen. Benjamin Mixon, commander of U.S. forces in northern Iraq, told CNN. He said that was evident from the fact Yazidis live in a remote part of Ninevah province that has been far from Iraq’s conflict.

Mixon said last month that he proposed reducing American troop levels in Ninevah and predicted the province would shift to Iraqi government control as early as this month. It was unclear whether that projection would hold after Tuesday’s staggering casualties.

Death estimates ranged widely.

Zayan Othman, health minister for Iraq’s nearby autonomous Kurdish region, said 250 bodies had been pulled from the rubble and some 350 people were injured.

But the death toll was put as high as 500 by some local officials, including Hashim al-Hamadani, a senior provincial security official; Kifah Mohammed, director of Sinjar hospital; and Iraqi army Capt. Mohammed Ahmed. They agreed with Othman that about 350 were wounded.

None of the officials provided information on how they arrived at their estimates. The figures could not be independently checked because the area was under curfew and casualties had been taken to numerous hospitals.

Also Wednesday, the top American commander in Iraq said he was preparing recommendations on troop cuts before he returns to Washington next month for a report to Congress, and believes the U.S. footprint in Iraq will have to be “a good bit smaller” by next summer.

But he cautioned against a quick or significant U.S. withdrawal that could surrender “the gains we have fought so hard to achieve.”

Gen. David Petraeus said the “horrific and indiscriminate attacks” that killed at the Yazidis, on Tuesday night were the work of al-Qaida in Iraq. That would bolster his argument, he said, against too quickly drawing down the 30,000 additional U.S. troops deployed in the first half of the year.

Petraeus, who wrote the Army’s book on counterinsurgency, said he and his staff were “trying to do the battlefield geometry right now” as he prepared his troop-level recommendations.