BAGHDAD — U.S. helicopters dropped 600 troops into two villages south of Baghdad before sunrise today, launching an assault on militants believed to be involved in the May kidnapping of three American soldiers, the military said.

The raids took place around 4 a.m. in the villages of Owesap and Betra, about 12 miles south of the Iraqi capital.

"These are areas where we believe al-Qaida was staging attacks, and we also believe they have ties to the May 12th attack," said Maj. Alayne Conway, spokeswoman for the Army's 3rd Infantry Division.

Three U.S. soldiers were kidnapped after their patrol was ambushed May 12 near Mahmoudiya, also south of Baghdad. Four other Americans and an Iraqi interpreter were killed in the attack, and an al-Qaida-linked group claimed responsibility.

Two soldiers remain missing, and the body of the third was found in the Euphrates River nearly two weeks later.

Today, two Chinook helicopters and eight Black Hawks dropped 600 U.S. troops into the targeted area, Conway said. F-16 fighter jets then dropped two bombs on an island in the Euphrates, to "deny the enemy terrain to escape," she said.

Some 150 Iraqi soldiers also participated in the operation, Conway said. By midday, there were no casualties on either side, she added.

Iraqi police said eight al-Qaida fighters were killed separately in a Shiite village near Muqdadiyah, about 60 miles north of Baghdad. Shiite townspeople, backed by police, drove the Sunni militants out of the village and killed eight of them, police said.

Meanwhile, a top British commander in southern Iraq said attacks plunged 90 percent across the country's south after Britain withdrew its troops from the main city of Basra.

The presence of British forces in downtown Basra, Iraq's second-largest city, was the single largest instigator of violence, Maj. Gen. Graham Binns told reporters Thursday on a visit to Baghdad's Green Zone.

About 500 British troops moved out of a former Saddam Hussein palace at Basra's heart in early September, joining some 4,500 at a garrison at an airport on the city's edge. Since that pullback, there's been a "remarkable and dramatic drop in attacks," Binns said.