"Reports constantly emerge of mortar attacks from US bases, but attacks hitting bases is not common, considering how heaviliy defended they are," he said.
US and Iraqi forces are currently battling fighters loyal to Muqtada al-Sadr, mainly in Sadr City, a stronghold of the Mahdi Army, as well as the southern city of Basra.

Monday's violence came a day after separate rocket attacks on the heavily protected Green Zone and a US military base in Baghdad killed three US soldiers and wounded at least 17 more.

The US fatalities were preceded by deadly clashes in Baghdad, just hours after the Iraqi government relaxed security measures around Sadr City and another Mahdi Army stronghold, Shula.
Officials at two local hospitals said women and children were among the dead.
US forces also carried out an air strike in Sadr City that killed "nine criminals", according to a military statement on Monday.
US commanders say barrages of rockets and mortars are being fired daily from Sadr City.