A roadside bomb killed four U.S. soldiers in Iraq on Saturday, and the bodies of 12 Iraqis who apparently were tortured and killed in captivity were discovered by police, most of them on the streets of Baghdad.

U.S. and Iraqi forces also fought an hour-long gunbattle with insurgents in Ramadi, a center of Iraq's Sunni Arab-dominated insurgency, and four militants were killed and two Iraqi soldiers wounded, American officials said.

Elsewhere, suspected insurgents also set off two bombs in a public market in northern Iraq, the second one timed to hit emergency crews arriving at the scene, and the blasts killed at least two Iraqis and wounded 17, police said.

The four U.S. Multinational Division-Baghdad soldiers were conducting a combat patrol south of the capital when the roadside bomb exploded and killed them. No other details were provided, including the name and rank of the deceased, while the attack was being investigated.

The deaths raised to 2,387 the number of members of the U.S. military who have died since the beginning of the Iraq war in March 2003, according to an Associated Press count.

In the market attack, the fist bomb exploded at 7:30 a.m. in the middle Muqdadiyah, a town about 60 miles north of Baghdad, causing a large fire, police in Diyala province said on condition of anonymity for security reasons. When fire engines arrived, the second bomb went off, killing a firefighter and a civilian, and wounding 17 civilians, police said.

The bullet-ridden bodies of 11 Iraqis were found in several locations in and around Baghdad, police said. Many of the victims were blindfolded with their hands and legs bound in rope. Some appeared to have been tortured, and one had been decapitated, police said.

In Kut, 100 miles southeast of Baghdad, police found a body floating in the Tigris River on Saturday. The victim showed signs of torture, including a severely damaged head, said Hadi al-Ittabi, an employee of the Kut Forensic Center.

Such killings are common in Iraq, and security forces often can't tell if the dead were the victims of insurgents, sectarian violence between Shiites and Sunnis, or criminals.

Also in Kut, a homemade bomb exploded early Saturday outside the home of Iraqi legislator Amir Najim al-Quraishi, a member of former Prime Minister Ayad Allawi's secular party, breaking glass windows and destroying a fence, but causing no casualties, a witness said.

In Baghdad's northern district of Azamiyah, unidentified gunmen in a speeding car sprayed a police patrol with machine gun fire, killing one officer, said police 1st Lt. Mohamed Khayon. In central Baghdad, gunmen killed a civilian riding in a car, said police Lt. Thair Mahmoud.

A roadside bomb exploded near a police patrol in the Harithiya neighborhood of southwestern Baghdad, wounding five civilians and a policeman, police 1st Lt. Maitham Abdul-Razzaq said.

In eastern Baghdad, a roadside bomb targeting another police patrol near al-Mashtal Bridge exploded, wounding two policemen, said police Lt. Bilal Ali.

In Mosul, 225 miles northwest of the capital, gunmen riding in a car wounded an Iraqi soldier on patrol, said police Maj. Gen. Wathiq Mohammed.

On Friday, at least 22 Iraqis were killed, including six in a car bombing in Tal Afar in western Iraq and six off-duty Iraqi soldiers were slain in Beiji in northern Iraq, police said.

The U.S. military announced that a Marine was fatally injured in combat Thursday in Anbar province.

An Australian soldier also was shot and killed in what the nation's army chief called a "tragic accident" inside Baghdad's fortified Green Zone, where Iraq's government and some officials and soldiers from the U.S.-led coalition are based.