Al Qaeda in Iraq offered personal details Tuesday about the man it said was the mastermind behind two of its first and most notorious homicide attacks — the August 2003 bombings of the U.N. headquarters in Baghdad and the main Shiite shrine in Iraq.

The planner of the attacks, Thamir Mubarak Atrouz, was killed by U.S. forces in April 2004, the group said in a "distinguished martyr's biography" posted on an Islamic radical Web forum.

Al Qaeda occasionally posts such biographies of its slain fighters, usually long after they are killed. Their authenticity cannot be independently confirmed.

The U.N. and Najaf bombings are seen as the first major attacks of Iraq's insurgency, which has continued unabated.

The Aug. 19, 2003, bomb attack on the U.N. headquarters in Baghdad killed 23 people, including the top U.N. envoy to Iraq, Sergio Vieira de Mello. More than 150 people were wounded.

Ten days later, a car bomb exploded outside the Shrine of Ali in the town of Najaf, south of Baghdad — one of Shiite Islam's holiest sites — killing more than 85 people, including the Shiite leader Mohammed Baqir al-Hakim.

Al Qaeda in Iraq, led by the Jordanian militant Abu Musab al-Zarqawi, has previously claimed responsibility for the attacks. But the Web biography was the first time it gave details of who was purportedly behind it.

It said Atrouz, from the town of Khaldiyah in the Sunni Arab province of Anbar west of Baghdad, was an officer in Saddam Hussein's army who fled Iraq to Saudi Arabia because of opposition to the Iraqi leader. He returned home just before the U.S.-led invasion of Iraq in March 2003 to fight the Americans.

"You need only to know about Hajji Thamir that he was directly in charge ... of two of Iraq's greatest operations in that year," it said, referring to him by the title given to Muslims who have made the pilgrimage to Mecca.

Atrouz was killed when U.S. troops attacked the insurgent stronghold of Fallujah in April 2004, after four U.S. security contractors were killed by a mob in the city.