Mortars and rockets fired by insurgents frequently hit the Green Zone
Three US service personnel have been killed and 31 wounded by rocket attacks on the Green Zone and a base elsewhere in Baghdad, the US military has said.
The rocket attack at 1530 (1230 GMT) on the Green Zone, which houses government offices and foreign embassies, killed two personnel and wounded at least 17.
A separate attack at the same time on a forward operating base in the Rustamiya district killed one and injured 14.
The attacks came after fighting between US and Iraqi forces and a Shia militia.
Twenty-two people were killed and more than 50 others injured in the clashes in the capital's eastern district of Sadr City, a stronghold of the Mehdi Army.
The militia's leader, radical Shia cleric Moqtada Sadr, has called for a mass demonstration in three days' time against the US military presence.
On Saturday, the Iraqi president, prime minister and other political leaders called for militias to be disbanded. Analysts said the call was aimed mainly at the Mehdi Army, which has recently been involved in heavy fighting with the security forces across southern Iraq.
Meanwhile, Iraqi security forces said they had found 42 university students unharmed after they were kidnapped near the northern city of Mosul earlier on Sunday.
The students were freed unharmed several hours after being kidnapped
The male students were on two buses ferrying them to Mosul from their homes in Shurkat, 70 km (40 miles) further south, when they were ambushed and captured.
Students who live outside Mosul often travel home on Thursdays, and return on Sundays.
Mosul has recently been the scene of extra security effort as US and Iraqi forces try to target al-Qaeda in Iraq fighters, who have regrouped in the area since being forced out of Baghdad and western Iraq.
Also on Sunday, hundreds of mourners attended the funeral of Father Youssef Adel in the capital's Karrada district.
The Assyrian Orthodox priest was killed on Saturday at his home.
One of the mourners, Midhat Faez, was quoted as saying the assassination was aimed at provoking conflict between Muslims and minority Christian community.
"As Christians, we are terrified and our numbers are gradually diminishing," he said.