Several mortar shells landed at the heavily fortified Halane base camp which houses AU forces headquarters in Mogadishu on Sunday evening.
A source within the facility told the shelling hit the facility and that there were a number of casualties.
The militant group Al-Shabaab claimed responsibility noting it fired 9 mortar shells.
The attack comes barely two weeks after a similar one in March.
A foreign national was reportedly injured in the shelling.