Pro-government forces backed by the AU force known as ATMIS launched an offensive last August against Al-Shabaab, which has been waging an insurgency in the fragile Horn of Africa nation for more than 15 years.

ATMIS said the Bulo Marer camp came under attack at 5 am (0200 GMT) by Al-Shabaab fighters militants "using Vehicle Borne Improvised Explosive Devices (VBIEDs) and suicide bombers".

"Reinforcements from ATMIS' Aviation Unit and allies managed to destroy weapons in possession of the withdrawing Al-Shabaab militants," it said in a statement.

The attack targeted Ugandan soldiers stationed in Somalia as part of ATMIS, Uganda Peoples' Defence Forces spokesman Felix Kulayigye said in a statement, adding that the military was "cross-checking" details.

The 20,000-strong ATMIS force has a more offensive remit than its predecessor known as AMISOM.

The force is drawn from Uganda, Burundi, Djibouti, Ethiopia and Kenya, with troops deployed in southern and central Somalia.

Its goal is to hand over security responsibilities to Somalia's army and police by 2024.

Al-Shabaab claimed via its communication channels that it had overrun the base and that it had inflicted a large number of casualties.

But Somali military commander Mohamed Yerow Hassan said the attackers had been repelled and the "situation is back to normal now."

"The terrorists were forced to retreat and flee," Hassan told AFP by telephone.

Al-Shabaab is known to exaggerate claims of battlefield gains in propaganda, while the governments of nations contributing troops to the AU force rarely confirm casualties.

Attacks on army bases in isolated parts of Somalia are difficult to independently verify.

ATMIS said that "everything is being done to bring the situation under control".

- Retaliatory attacks -

Last year, Somalia's President Hassan Sheikh Mohamud launched an "all-out war" on the militants, rallying Somalis to help flush out members of the jihadist group he described as "bedbugs".

In recent months, the army and militias known as "macawisley" have retaken swathes of territory in the centre of the troubled country in an operation backed by ATMIS and US air strikes.

The US Africa Command on Monday said it had carried out a strike the weekend before in Jilib in Somalia's south, and that initial assessments indicated no civilians were harmed.

Despite the gains by the pro-government forces, the militants have continued to strike with lethal force against civilian and military targets.

In the deadliest Al-Shabaab attack since the offensive was launched, 121 people were killed in October in two car bomb blasts at the education ministry in Mogadishu.

In a report to the UN Security Council in February, UN chief Antonio Guterres said that 2022 was the deadliest year for civilians in Somalia since 2017, largely as a result of the Al-Shabaab attacks.