Baghdad, Iraq ? Residents returned to Baghdad’s streets Monday after a two-day lockdown during a Shiite religious commemoration that was disrupted by sniper attacks on pilgrims in another episode of sectarian bloodletting.

Two U.S. Marines and a sailor were killed Sunday in combat in Anbar province, the stronghold of the Sunni Arab insurgency west of Baghdad, the U.S. military said.

The Iraqi government said 20 people were killed by the snipers who hid in buildings and sprayed bullets into Shiite religious processions Sunday. The U.S. military, however, said only five people were killed. The discrepancy in the toll could not be immediately reconciled.

On Monday, major intersections were clogged with vehicles that had been ordered off the streets since Friday night to prevent car bomb attacks on pilgrims. A virtual curfew had gripped the capital on Saturday and Sunday, and few people were seen except pilgrims.

Prime Minister Nouri al-Maliki, a Shiite, thanked the armed forces for preventing major attacks. “We condemn strongly the terrorists attacks committed by the terrorists against innocent civilians,” he said in a statement.

About 12,000 extra U.S. and Iraqi soldiers have been deployed to Baghdad in recent weeks as part of a security crackdown on a surge of insurgent attacks and sectarian bloodshed in the capital.

Hundreds of thousands of Shiites had marched in processions to the shrine of Imam Moussa Kadhim, an 8th century saint, in Kazimiyah in north Baghdad. Some processions were ambushed by snipers when they passed three or four Sunni neighborhoods.

An Iraqi girl waits in line Monday for fuel in Baghdad, Iraq. Iraq plans to build several new oil refineries and upgrade existing ones to start exporting gasoline and other byproducts by 2010, oil minister Hussain al-Shahristani said Monday.

“I was walking and someone got shot in front of me. It wasn’t random fire, it was a clear sniper attack,” said Mohammed Jassim, 32.

He said he could hear the faint crack of shots over the noise of the procession. “People panicked and started yelling: ‘It came from here, no from there.”‘

About 300 people were injured, mostly when they fell while running to escape gunfire in Sunni Arab-dominated areas along the parade routes. In one neighborhood, gunmen hid behind tombstones at a Sunni cemetery.

Still, the day’s main ceremonies went off peacefully at the golden-domed shrine where Kadhim is buried. Shiites believe that Kadhim, who died in A.D. 799, was poisoned in prison by a Sunni caliph.

The Sunni-Shiite rivalry, which predates Kadhim, continues to this day. Extremists among the two communities have been carrying out retaliatory attacks since the Feb. 22 bombing of a Shiite mosque in Samarra.

Despite the sense of relative normality, Baghdad remained on guard Monday against possible attacks on the mile-long lines of cars at gasoline stations, a favorite target of insurgents. Street cleaners and municipal workers carefully sifted through garbage, in which improvised booby-trapped bombs have been placed in the past.

Last year’s Kadhim commemoration also was marred by deaths when rumors of suicide bombers triggered a mass stampede on a bridge across the Tigris River. The government said about 1,000 people died in the worst single day death toll since the U.S.-led invasion in March 2003. Shiites were prevented from assembling in large numbers at religious ceremonies during Saddam Hussein’s Sunni-dominated regime. But since his ouster, Shiite politicians and religious leaders have encouraged huge turnouts as a demonstration of the majority sect’s power.