A military official says two U.S. troops were killed and 17 wounded when rockets struck the Green Zone in central Baghdad.
The official says another American service member died and 14 were wounded in another attack on a military base in the southeastern area of Rustamiyah.
The official spoke on condition of anonymity for lack of authorization to release the information.
The attacks come amid fierce clashes between Shiite militia fighters and U.S.-Iraqi forces.
In Other Developments:
The U.S. military said that fighting broke out overnight in Sadr City, a stronghold of anti-American cleric Muqtada al-Sadr's militants. Officials at two local hospitals said 22 people were killed and 92 wounded.
The officials, who spoke on condition of anonymity because they were not authorized to talk to the media, did not say whether the casualties were civilians or fighters. U.S. and Iraqi forces released no information about the casualties.
A police officer said that a U.S. Stryker armored personnel carrier was damaged in the fighting, which continued with sporadic exchanges of fire through Sunday morning.
Two armored Humvee vehicles and two trucks belonging to the Iraqi army were also destroyed, said the officer, who also spoke on condition of anonymity because he was not authorized to talk to the media.
The U.S. military said it had no information about a Stryker being damaged.
During the operation, nearly 1,000 government soldiers and policemen deserted and handed over their weapons and vehicles to the Mahdi fighters.
"It was obvious that there was negligence among some members of our security forces and this issue will be dealt with according to the law," Tahseen al-Sheikhli, spokesman for the Baghdad security operation, told reporters Sunday.
Although scattered clashes continued between his fighters and Iraqi security forces, the Iraqi government relaxed security measures Saturday around the Mahdi Army strongholds of Sadr City and the Shula neighborhood.
A vehicle ban remains in effect as part of a curfew imposed on Baghdad after fighting broke out between government forces and Shiite militants March 25. The curfew has been lifted in the rest of Baghdad.
The hijacked bus was then driven onto a farm road, where all the students were released after the gunmen made sure they were not members of the security forces, Abdul-Sattar said.
One of the mourners, Midhat Faez, said the assassination was aimed at provoking conflict between Muslims and the tiny Christian community.
"As Christians, we are terrified and our numbers are gradually diminishing," Faez said.