Mahir Ahmad Mahmud al-Zubaydi, also known as Abu Assad or Abu Rami, allegedly directed the insurgent cell believed to be responsible for nearly simultaneous car bomb and suicide attacks Thursday, according to the statement.
Iraqi police and hospital officials have said some two dozen people were killed in Thursday's attacks targeting two Shiite mosques in Baghdad.
The victims were attending prayers marking Eid al-Fitr, the religious holiday that comes at the end of the Islamic fasting month of Ramadan.
Al-Zubaydi was one of the most senior insurgents to be killed by U.S. forces as they seek to shore up recent security gains that have driven the level of violence to its lowest point in more than four years.
His death would be a major blow to al-Qaida in Iraq even as the group's recruiting efforts have been "severely curbed" by a decision by many Sunnis to join forces with the Americans in the fight against it, military spokesman Rear Adm. Patrick Driscoll said.
"His removal from the AQI network will send shockwaves through Baghdad's terrorist bombing networks," Driscoll said in the statement.
The military also blamed al-Zubaydi for responsible for several car bombings and mortar attacks in Baghdad's main Shiite district of Sadr City in 2006 and 2007, including a series of blasts that killed more than 200 people on Nov. 23, 2006.
That was one of the deadliest attacks to strike the Iraqi capital amid rampant sectarian violence and attacks against U.S. forces.
Al-Zubaydi also was believed to have planned and participated in abductions and videotaped executions, including one in which he is personally seen shooting one of four kidnapped Russians, according to the statement.
The Russian embassy workers were abducted in June 2006 after an attack on their car in Baghdad's Mansour neighborhood. They were later killed, along with a fifth Russian.
