Updated

Mortar rounds hit a Shiite enclave south of Baghdad on Friday, killing at least three people in the latest sign of violence returning to areas that U.S. and Iraqi forces have considered largely stable.

The attack in the Jisr Diyala district — although small compared with recent bombings — reinforced worries that security forces may need to shift attention back to areas that have been relatively quiet in recent months even as they battle to control the last insurgent strongholds north of Baghdad in Diyala and Mosul.

It also raised concerns about Iraq's ability to maintain security in Baghdad and other key areas after the U.S. military withdraws from major cities by the end of June.

Police and hospital officials said the mortar attack in Jisr Diyala killed at least three people and wounded about 10 others. The district in southeastern Baghdad is primarily Shiite, but is surrounded by heavily Sunni areas.

The officials spoke on condition of anonymity because they were not allowed to release the information.

The attack comes as Iraqi and U.S. forces face a spike in violence, including several high-profile bombings.

On Thursday, a suicide bomber struck an Iraqi military base in Habbaniyah, about 45 miles west of Baghdad. There were conflicting account of casualties, including some indicating fatalities. But the Defense Ministry spokesman, Maj. Gen. Mohammed al-Askari, said 38 Iraqi soldiers were wounded but only the bomber died.

At least 37 people have been killed in four major attacks on Iraqi security forces since April 10, when a suicide truck bomber blasted the regional police headquarters in Mosul. Five American soldiers and two Iraqi policemen were killed in the Mosul blast.

In Washington, Defense Department spokesman Bryan Whitman said Thursday that the latest bombings show "there is still the ability to conduct these spectacular and lethal attacks."