Almost simultaneous suicide bomb blasts targeted the base in the southern city of Baardhere, which hosts both Ethiopian and Somali troops, triggering heavy gunfire, sources said.
"The first explosion which is presumed to have been carried by a suicide bomber targeted the entrance of the military base in Baardhere, which lies in Jubaland state about 450km south of the capital, Mogadishu.
"The second blast occurred in the same area within a few minutes after the first one, there are some casualties but we don't have the details so far," he said, adding that the situation in the area was "now normal."
Local resident Bare Hassan reported "heavy gunfire" after the first blast at the base in Baardhere.
There was no immediate information about any casualties from the attack, which was claimed by al-Shabab, an al-Qaeda affiliated group that has been waging a bloody insurgency against the fragile central government for more than 15 years.
Al-Shabab has continued to launch deadly attacks in Somalia in the face of a major offensive by pro-government forces backed by the A.U. force known as ATMIS against the jihadist group.
Only last month, 54 Ugandan peacekeepers were killed when al-Shabab fighters stormed an A.U. base located southwest of Mogadishu in one of the deadliest attacks since the offensive was launched last year.
Earlier Wednesday, the African Union Transition Mission announced it had started to reduce troop numbers in Somalia in line with U.N. Resolutions "which mandate ATMIS to drawdown 2,000 soldiers by the end of June 2023".
ATMIS in April last year replaced the previous mission known as AMISOM, which had a force of about 20,000 drawn from several nations including Burundi, Kenya and Uganda.
It said it handed over a base operated by Burundian forces in Hirshabelle state in south-central Somalia to the Somali National Army.
ATMIS has a more offensive remit than its predecessor, and calls for security to be assumed by Somalia's army and police force by the end of 2024.
As al-Shabab attacks surge despite the military operation, President Hassan Sheikh Mohamud earlier this week sacked the head of the army, Odowaa Yusuf Rageh, and named Ibrahim Sheikh Muhidin as his successor.
Forum