BAGHDAD — A U.S.-led raid and airstrike targeting networks allegedly smuggling weapons and fighters from Iran killed 32 suspected militants early today in Baghdad's Shiite stronghold of Sadr City, the military said.

Word of the raid came after Iraqi police in Sadr City had said that a bombardment by U.S. helicopters and armored vehicles had killed nine civilians, including two women, and wounded six others. The police also said 12 people were detained.

The U.S. military said 12 suspects were detained during the raids.

"The individuals detained and the terrorists killed during the raid are believed to be members of a cell of a Special Groups terrorist network known for facilitating the transport of weapons and explosively formed penetrators, or EFPs, from Iran to Iraq, as well as bringing militants from Iraq into Iran for terrorist training," the military said.

Meanwhile, Iraqi authorities clamped a three-day driving ban on the capital and erected new checkpoints, while thousands of Shiite pilgrims began their annual trek toward a mosque in northern Baghdad to mark the anniversary of the death of one of Shiite Islam's key saints.

First-aid tents stocked with coolers of bottled water or offering food lined the streets as authorities scrambled to prevent a catastrophe from marring the ceremonies honoring Imam Moussa ibn Jaafar al-Kadhim, one of 12 principal Shiite saints who died in the year 799.

More than a million Shiite faithful — flogging themselves with iron chains and slicing their foreheads with swords — are expected to process Thursday toward the shrine of Imam al-Kadhim in Baghdad's Shiite Kazimiyah neighborhood.

The self-flagellation slowly turns their white cloaks red with blood in a ritual of grief banned under Saddam Hussein.

Sunni insurgents often target such gatherings. In 2005 the march was hit by tragedy, when thousands of Shiite pilgrims, panicked by rumors of a suicide bomber, broke into a stampede on a bridge. About 1,000 people died.

The top U.S. ground commander in the area, Task Force Justice leader Lt. Col. Steve Miska, said today that hundreds of additional Iraqi security forces had been deployed in Kazimiyah, but that American troops would stay away from the shrine out of religious sensitivity.

"There's paranoia surrounding this shrine. If anything happened here, it'd make the Golden Dome look like a precursor," Miska said, referring to the al-Qaida bombing of Samarra's Askariya shrine, which destroyed the mosque's golden dome and set off a wave of sectarian bloodletting that continues today.

Iraqi Prime Minister Nouri al-Maliki, meanwhile, arrived in Iran for talks expected to focus on bilateral relations and improving the security situation in Iraq. It was the Iraqi premier's second visit to Tehran in less than one year.

"We are here today to boost commercial and security relations with neighboring countries," al-Maliki told The Associated Press on the plane to Iran. He said he would focus on overcoming "terrorism challenges" in the region.

Iraq, which like Iran is majority Shiite, has managed a difficult balancing act between Tehran and Washington since the U.S.-led invasion in 2003, trying to maintain good relations with its powerful neighbor while not angering the Americans.

The U.S. has accused Iran of providing money and weapons to Shiite militias in Iraq. Iran denies the charges,

Baghdad residents awoke to find themselves facing a vehicle ban earlier than expected.

The Iraqi military spokesman Brig. Gen. Qassim al-Moussawi announced a curfew banning all cars, trucks, motorcycles and carts from moving in city streets that had been slated to begin at 10 p.m. today would begin 5 a.m. instead. It was to last until 5 a.m. Saturday.

Soldiers were deployed about 100 yards apart on streets in western Baghdad and traffic was barred by barbed wire and warning signs.

Pilgrims wearing traditional white frocks and waving green Shiite flags walked from all points of the capital toward the golden-domed mosque where al-Kadhim is believed to be buried in the northern neighborhood of Kazimiyah. Many men wore wet towels on their heads for relief from the heat.

By this morning, some 1,500 pilgrims had already passed through one of several checkpoints into the area, according to an Iraqi police lieutenant who identified himself only as Fadil, because of security concerns.

Some 400 plainclothes Iraqi agents, part of a mostly Shiite organization called the Public Order Committees, would take up positions at checkpoints, Miska said.

U.S. officials said more than a million pilgrims were expected Thursday in Kazimiyah, but some Iraqi officials put the figure at four million.