The Sunni insurgent group known as 1920 Revolution Brigades said its military leader, Harith Dhaher al-Dhari, was killed in Abu Ghraib just west of Baghdad. An Iraqi district official said attackers fired rocket-propelled grenades at the man's car, but the US military said suicide car bombers attacked his house.

The attack came as the Shiite-led government of Prime Minister Nouri al-Maliki is reportedly making progress rallying Sunni Arab tribesmen into joining the fight against al-Qaida members in Anbar province west of the capital. Al-Dhari's group is among those rumored to be taking part in secret talks with the government.

Al-Qaida has responded with bomb attacks targeting leaders and key supporters of the tribes allied against them.

In the northern city of Kirkuk, police 1st Lt. Marewan Salih said the slain nuns - 79-year-old Margaret Naoum and 85-year-old Fawzeiyah Naoum, 85 - were killed in their home near the Cathedral of the Virgin. They lived alone and there was no sign of a robbery, he said.

Naoum was stabbed seven times as she stood in the garden just outside the house, while Naoum was stabbed three times while lying on the sofa inside as she was recovering from eye surgery last week.

Chaldean Catholics are an ancient Eastern rite now united with Roman Catholicism. Adherents live mainly in Syria, Turkey, Iran and Iraq and most speak a dialect of Turkish.

In Baghdad, US Charge d'Affairs Daniel Speckhard said a rocket attack killed an American contract worker in the Green Zone, the heavily fortified area that is home to the US Embassy and Iraqi government offices. The US military said an American soldier also was killed and a second soldier suffered unspecified wounds.

The identities of the dead were not released, and US officials did not give the nationalities of the four wounded contract workers.

It was the second rocket attack on the zone in less than a week. A Katyusha rocket exploded just 50 yards from UN Secretary-General Ban Ki-moon as he spoke with reporters there Thursday during an unannounced visit to the city.

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