Baghdad, Iraq ? The Iraqi government Friday imposed a two-day vehicle ban in the capital, an effort to avoid bloodshed during a major Shiite festival this weekend.

The vehicle ban, which includes most of Baghdad, will be in effect until 6 a.m. Monday.

During the festival last year, pilgrims crossing a bridge over the Tigris River stampeded after rumors spread that a suicide bomber was among them. Some 1,000 people – many of them women and children – drowned or were trampled to death in what remains the bloodiest day since the American-led invasion.

This year, authorities estimate that more than 1 million people may attend the festival, which marks the death in A.D. 799 of Imam Musa Kadhim, one of 12 major Shiite saints.

On Friday, as pilgrims arrived in the city, they found the capital locked down with ubiquitous checkpoints, concrete blast walls separating neighborhoods and thousands of troops patrolling the streets.

As they walked toward a blue-domed shrine in eastern Baghdad where Kadhim is buried, violence continued in and outside the capital.

Authorities said gunmen shot and killed seven pilgrims walking along a highway in western Baghdad.

Just north of Baghdad near Baqouba, a Sunni couple were killed by gunmen.

In Dora, one of the most lawless areas in the city, a suicide car bomber detonated explosives near a house of worship, injuring three.

Meanwhile, the U.S. military announced that the Iraqi army had captured three men suspected of ambushing Iraqis in July at a checkpoint in the Jihad neighborhood.

During the last 12 months, U.S. troops handed over swaths of the capital to Iraqi forces. In most neighborhoods, security deteriorated rapidly. In an effort to regain control of the capital, the U.S. military recently announced a new security plan in which U.S. troops would once again become a more active presence in the city. The stepped up security effort – dubbed Operation Forward Together – involves 12,000 American and Iraqi troops.

In an office affiliated with the Shiite cleric and militia leader Muqtada al-Sadr in western Baghdad, soldiers from the 172nd Stryker Brigade on Friday found mortars and three surface-to-air 57 mm rockets, one rigged as a roadside bomb, according to the military.

U.S. officers suspect al-Sadr’s al-Mahdi army is behind many kidnapping and killings of Sunnis as well as attacks against Americans. Some al-Mahdi army members have infiltrated the Iraqi Army and police.