BAGHDAD — A suicide bomber dressed in a woman’s robe detonated explosives yesterday in a heavily guarded Sunni area of Baghdad, killing the deputy leader of the neighborhood’s American-backed security volunteers who had turned against Al Qaeda, Iraqi officials said.

Six bodyguards of the deputy leader of the “awakening council” in Baghdad’s Azamiyah district, Farooq al-Obeidi, also died in the blast.

The explosion occurred as they were seated on chairs near a checkpoint near the Abu Hanifa mosque in the former insurgent stronghold, police and Iraqi army officials said.

The assailant, wearing a black abaya robe, walked up to Obeidi’s party and detonated the explosives, the officials said on condition of anonymity because they were not supposed to talk to press.

“While I was shopping just across the street, I heard a huge explosion,” a member of Obeidi’s group, Omar Qassim, said. “Body parts were flying through the air. I immediately realized that Farooq’s party was targeted and he was probably dead.”

Some of the officials said the attacker was a woman. But one of them said the attacker was a man who probably wore the flowing garment to conceal the explosives.

Officials at a nearby hospital said about 20 people were wounded. They spoke on condition of anonymity because they were not authorized the release information to press.

Such attacks have become rare in the center of Azamiyah since the American military built a concrete wall around the heart of the north Baghdad neighborhood, where Saddam Hussein took refuge when the city fell to American forces in April 2003.

Although Azamiyah was once a center of resistance to America and its Shiite allies, many local Sunnis later abandoned the insurgency and joined the awakening council, which provides security there alongside Iraqi soldiers and police.

Al Qaeda in Iraq has often targeted leaders of awakening councils. But an aide to Obeidi, Khalil Ibrahim, said the attack could have been carried out by rivals within the council itself.

“We had received information that we would be targeted by groups within Azamiyah and within the awakening movement itself,” he said, refusing to elaborate.

A senior police official also said it was unlikely that explosives could have been smuggled into the area because of security checks around the wall and said he suspected the attack could have been part of a power struggle within the council.

He spoke on condition of anonymity because the investigation had only just begun.