BAGHDAD - A suicide bomber strapped with explosives struck a group of American soldiers standing outside a city council meeting north of Baghdad yesterday, killing six people, including one of the soldiers, and marring the celebration of a major Muslim holiday.

The midday explosion was a painful reminder of the dangers that persist in many parts of Iraq and remain particularly potent in Diyala province.

The blast, east of the provincial capital of Baqubah in the tribal village of Kanaan, killed at least five Iraqis and wounded a sixth and injured 10 U.S. soldiers, according to U.S. military officials.

Capt. Qasim Ibrahim Muhammad, an Iraqi police official in Kanaan, said the bombing took place outside a building where Sunni men were volunteering for the local defense forces that have become so prevalent. He said 10 Iraqis were killed and eight wounded.

These predominantly Sunni defense forces have come under increasing attack because of their alignment with U.S. soldiers against insurgent groups such as al-Qaeda in Iraq.

In Diyala, some of the volunteers are former members of the 1920 Revolution Brigades, a Sunni insurgent group that has fought street battles against al-Qaeda in Iraq.

A spokesman for the volunteers in Diyala, Farhan al-Buhrizawi, said that a leader of the 1920 Revolution Brigades, Naseer al-Maamouri, and his bodyguard and driver also were found shot dead yesterday in Baqubah. They had been kidnapped the night before, he said.

The violence came as Sunnis in Iraq celebrated Eid al-Adha, a holiday commemorating Abraham's willingness to sacrifice his son. Many Shiites began celebrating the holiday last Friday.

Iraqi police said at least five people were killed in Baghdad bombings, but the bloodshed has paled in comparison to last year's holiday, when widespread killing followed Saddam Hussein's hanging.

Also in Diyala province, the U.S. military said American soldiers killed 24 suspected insurgents and detained 37 people during a four-day operation this month and found weapons, mass graves and three buildings that they believed were used for torturing prisoners.

The rooms in the buildings "had chains, a bed - an iron bed that was still connected to a battery - knives and swords that were still covered in blood," said Army Maj. Gen. Mark P. Hertling, the top U.S. commander in northern Iraq.

Scrawled in white paint above a bed in the torture area was a Koranic phrase in Arabic normally used to welcome a guest. But the context suggested only sadistic mockery: "Come in, you are safe."

The floor was littered with food wrappers, soda bottles and electric cables that led to a metal bed frame, presumably where detainees were given electric shocks, according to the U.S. account of the discovery during a Dec. 8-11 mission. Nearby were nine graves containing the remains of 26 people, Hertling said. Villagers knew about the torture site but did not tell authorities, as they were afraid of reprisals, a police officer said. He spoke on condition of anonymity as he was still afraid of being targeted by extremists. He said he thought the chamber had been used for a year.

This article contains information from the Associated Press.