Another 40 percent of the Iraqi security forces walked off the job because they didn't want to fight fellow Iraqis, said Maj. Gen. Martin Dempsey, commander of the U.S. Army's 1st Armored Division.
Dempsey said it was "very difficult" to convince security forces that the insurgents they are fighting are "killing fellow Iraqis and fellow Muslims," he said in an interview beamed by satellite from Baghdad to Washington.
The failure of Iraqi security forces to fight is significant because Washington's exit strategy depends on moving U.S. troops out of cities and over responsibility for security to Iraqi forces.
Meanwhile, coalition officials said Thursday that it was too early to blame al Qaeda for simultaneous suicide car bombings in Basra that killed dozens of people, reviving the issue of how much of a role foreign militants have in Iraq's violence.
A spokesman for British forces responsible for the Basra area gave a death toll of 50 — 20 of them children — for Wednesday's blasts, lower than the toll of 68 reported by Basra's governor.
In other developments:
In Fallujah, insurgents attacked U.S. Marines, prompting a clash that killed 20 guerrillas. And U.S. military officials said residents were turning in mostly unusable weapons, undermining a crucial part of an agreement aimed at ending the fighting and lifting the U.S. siege of the city.
"These may be early indications that the insurgents may not be living up to the requirements of the agreement," said Marine Lt. Col. Brennan Byrne.
Fighting in Fallujah has killed at least seven U.S. Marines and more than 600 Iraqis, mostly civilians, according to the city hospital.
The links between foreign fighters and homegrown Iraqi guerrillas — and question of which are in the forefront of Iraq's violence — has long been unclear. Out of 2,000 suspected guerrillas held by U.S.-led forces, only 50 are foreigners.
It was still too early to say who was behind the Basra attacks, a spokesman for the British forces responsible for the area said Thursday.
"We can't discount al Qaeda, we can't discount former regime loyalists. It is too early to start speculating," Capt. Hisham Halawy, spokesman for the British forces, said in Kuwait on Thursday.
Suicide attackers detonated five car bombs — all but one of them simultaneously — targeting police buildings in Basra, Iraq's second largest city Wednesday, striking rush-hour crowds just as buses carrying kindergartners and school girls were passing by.
Police discovered two car bombs before they were detonated and arrested three men in the vehicles, said Basra Gov. Wael Abdul-Latif
Abdul-Latif said 68 people were killed, including 16 children, and he said he suspected al Qaeda was behind the attack.
But Halawi said a review of the hospitals revised the numbers. "After we got to hospitals, the number of those killed is 50, including 20 children," he said, adding that five coalition soldiers were wounded, one seriously.
Basra is overwhelmingly Shiite and the last major suicide attack also targeted Shiites: a series of suicide bombers who near simultaneously detonated explosives strapped to their bodies among thousands of pilgrims at holy shrines in Karbala and Baghdad on March 2. At least 181 people were killed.
U.S. coalition officials said they believed those attacks were planned by a Jordanian al Qaeda linked militant, Abu Musab al-Zarqawi, who they say plans a campaign of massive attacks on Shiites in order to spark a civil war between Iraq's Shiite Muslim majority and Sunni minority.
Abdul-Latif pointed to the similarities between that attack and the Basra bombings in making his link to al Qaeda.
But a U.S. counterterrorism official said it was "just premature to draw any conclusions."