BAGHDAD — A suicide bomber killed five American soldiers on a foot patrol today after detonating his explosives vest in central Baghdad, the American military said, the deadliest attack on American forces in Iraq in more than a month.

Four of the soldiers died at the scene and the fifth died later from wounds, the military said in a statement. The blast also wounded three American soldiers and an Iraqi interpreter, the military said.

A military spokesman, Major Mark Cheadle, said that “it was reported to us as a suicide bomber.”

An Iraqi police officer at the scene, speaking on condition of anonymity because he was not authorized to speak to the media, said two civilians also were killed and another eight wounded in the attack.

It was the deadliest attack since January 28, when five American soldiers were killed in a roadside bomb in the northern city of Mosul.

Today’s deaths brought the number to 3,979 members of the American military who have died since the beginning of the Iraq war in March 2003, according to an Associated Press count.

Meanwhile, a female suicide bomber today killed the head of a local group of Sunni fighters northeast of Baghdad who had turned against Al Qaeda insurgents, the leader’s brother and a provincial police official said.

Sheik Thaeir Ghadhban al-Karkhi, his 5-year-old niece, a 24-year cousin, and a security guard were killed in the blast in Diyala province, where violence has persisted despite drops in other parts of Iraq.

The sheik’s brother, Duraid Mahmoud, said he witnessed the attack inside his brother’s home. A provincial police official, speaking on condition of anonymity because he was not authorized to release the information, confirmed the attack.

The woman, wearing an explosives belt, entered al-Karkhi’s home in the predominantly Sunni town of Kanaan, 13 miles east of Baqouba.

There was no immediate claim of responsibility. But Al Qaeda in Iraq has been targeting fellow Sunni Arabs who have taken up arms against the militants and joined the so-called awakening councils like the one al-Karkhi led.

The councils are made up of American-backed former insurgents who have risen up against Al Qaeda’s brutality and strict Islamic codes of conduct it was trying to impose on local populations.

The American military said it was looking into the incident but did not immediately have any details.

Mr. Mahmoud said the bomber had visited the sheik’s house yesterday, claiming that her husband had been kidnapped and asking for help. Mr. Mahmoud said his brother told the woman to return today.

“She came back this morning and nobody checked her. She had an appointment with the sheik and the guards told her to go and knock on his door,” Mr. Mahmoud said.

The woman was ushered into the house and blew herself up once she got close to the sheik, he said, adding that the sheik’s 5-year-old niece and a security guard were also killed.

One of the men wounded in the attack — the son of a cousin of the sheik — later died at the hospital, according to a hospital official who spoke on condition of anonymity because he was not authorized to speak to the media.

Hours after the attack, mourners packed al-Karkhi’s home, weeping over the sheik’s body, which had been wrapped in a blue blanket and placed in a black, wooden coffin.

Female suicide bombers have been involved in at least 19 attacks or attempted attacks since the war began, including the grisly bombings of two pet markets in Baghdad that killed nearly 100 people on February 1.

A female suicide bomber last struck in a Shiite neighborhood in Baghdad on February 17, detonating herself after soldiers fired three bullets at her. Causalities were disputed in that attack, with Iraqi officials saying four people were killed, while the American military said only the bomber died.

In southern Iraq, the body of a doctor who was kidnapped yesterday was found.

Khalid Nasir al-Miyahi, a neurologist working at a hospital in Basra, was kidnapped by unidentified gunmen, police said. His body was found in a central area of the city.

According to figures from the Iraqi Health Ministry released earlier this year, 618 medical employees, including 132 doctors, as well as medics and other health care workers, have been killed nationwide since 2003. Professionals from many fields have been targeted in Iraq’s violence.

Hundreds, possibly thousands, of other medical personnel are believed to have fled to Iraq’s northern autonomous Kurdistan region and neighboring countries.

Elsewhere, two nearly simultaneous attacks took place in Baghdad’s Shaab neighborhood, one of the capital’s most dangerous areas and a center for outlawed Shiite fighters.

The first attack was a roadside bomb that targeted an American patrol around 9:15 a.m., local time, police said. One civilian was wounded.

There was no immediate word on any American causalities; the military did not immediately respond to an e-mailed request for information.

The second attack took place five minutes later, when a parked car bomb detonated, wounding six civilians and damaging several nearby shops, police said.