The military said the patrol was struck in a pre-dawn explosion near Mahmoudiya, about 20 miles south of Baghdad — an al Qaeda area where two U.S. soldiers were found massacred after disappearing at a checkpoint nearly a year ago.
A nearby unit heard the blast and the search was launched after communication could not be established with the patrol, the military said, adding that a drone plane later observed two burning vehicles after about 15 minutes.
An emergency response unit arrived at the scene about an hour later and found five members of the team killed and three others listed as duty status and whereabouts unknown.
U.S. military sources tell CBS News that it may take DNA tests to make final identifications, although an Iraqi Army interpreter is believed to be among those killed, reports CBS News correspondent Mark Strassmann.
Checkpoints were established throughout the area, while helicopters, jets and unmanned drones buzzed overhead.
But such a search is a nightmare scenario for the U.S. military: The soldiers are facing hostile terrain and have no idea whether the missing are captured, wounded or both, reports Strassmann.
AP Television News footage showed Iraqi soldiers picking through cattails and other weeds as they searched fields and canals for clues.
Lt. Col. Christopher Garver, a U.S. military spokesman, said the search would continue throughout the night.
"A lot of our vehicles have thermal capabilities, which sometimes work better at night than they do during the day," he said.
In Other Developments:
The attack in Makhmur, 30 miles south of Irbil, targeted the office of the Kurdistan Democratic Party of Massoud Barzani, leader of the autonomous Kurdish region in northern Iraq. Makhmur is not part of the Kurdish-controlled areas of northern Iraq.
The military refused to specify whether the Iraqi interpreter was among those killed or among the missing or give more details about where the bodies were found.
An Iraqi army officer, who was familiar with the search but spoke on condition of anonymity because he was not authorized to disclose the information, said he saw five badly burned bodies inside a Humvee at the attack site, suggesting the remains may not have been recognizable.
The Iraqi officer said U.S. troops singled out seven suspects out of as many as 50, including a wounded man who was hiding in a house and confessed to participating. He said most of the houses searched near the attack contained only women and children because the men had fled after hearing news of the attack, fearing arrest.
"I was in my cucumber field when I heard a big explosion followed by shootings. I ran toward my house because I was afraid that I would be arrested if spotted in the field," Mizaal Abdullah, a 37-year-old farmer who was in the custody of the Iraqi army, said by telephone. "This is the third time that I have been arrested. Each time, the real attackers flee the area and innocent people like me get arrested."
The attack occurred at 4:44 a.m. about 12 miles west of Mahmoudiya, a town of about 65,000 people located in a Sunni area dubbed the "triangle of death" for the frequent attacks against Shiite civilians and U.S. and Iraqi forces.
On June 16, 2006, two American soldiers — Pfc. Kristian Menchaca of Houston and Pfc. Thomas Tucker of Madras, Oregon — went missing after their Humvee was ambushed at a checkpoint near Youssifiyah, to the north of Mahmoudiya.
Their bodies were found days later, tied together with a bomb between one of the victim's legs, but the remains were not recovered until the next morning, after an Iraqi civilian warned that bombs had been planted in the area.
A third soldier, David J. Babineau, 25, of Springfield, Massachusetts, was found dead at the scene of the attack.
Five U.S. soldiers also have been charged in the rape of a 14-year-old Mahmoudiya girl and the killing of her and her entire family, and three have pleaded guilty in the March 12, 2006, attack, which was initially blamed on insurgents.
More than 3,380 members of the U.S. military have died since the Iraq war started in March 2003, according to an Associated Press count. But few have been kidnapped in Iraq, due largely to strict military procedures for those on patrol or at checkpoints.
U.S. troops in Iraq travel in groups of armored vehicles, usually Humvees, and procedures are in place to keep track of troops so no one is left behind, either by accident or because of the chaos of war.
The last U.S. soldier known to have been captured was Ahmed Qusai al-Taayie, whose name is also spelled Ahmed Kousay Altaie, an Iraqi-born reserve soldier from Ann Arbor, Michigan, who was abducted while visiting his Iraqi wife on Oct. 23 in Baghdad.
Sgt. Keith M. Maupin of Batavia, Ohio, was taken on April 9, 2004, after insurgents ambushed a fuel convoy. Two months later, a tape on Al-Jazeera purported to show a captive U.S. soldier being shot, but the Army ruled it was inconclusive proof of Maupin's death. He is listed as missing.
Capt. Michael Speicher, a Navy pilot, also has been missing since the 1991 Persian Gulf War.