"Small rockets" hit the Iraqi base hosting American and other troops in Baghdad's Green Zone early Sunday, a U.S. military spokesperson confirmed in a statement.

Details: The attack at the base hosting International Coalition for Operation Inherent Resolve troops occurred just before 3:30 a.m., said Col. Myles B. Caggins III. There were no casualties and an investigation has been opened into the incident, he added.

The big picture: No group has claimed responsibility for the blasts, which come just over a month after Iran's Jan. 8 missile attack on U.S. bases in Iraq.

109 American troops sustained traumatic brain injuries as a result of that attack, the State Department said last Monday.

Editor's note: This article has been updated with more details on the attack and context.