“There was an attack this morning at our base… by elements of al-Shabab,” said Uganda People’s Defence Force (UPDF) deputy spokesman Deo Akiiki.
The army base is located in Bulo Marer, 120 kilometres (75 miles) southwest of the capital Mogadishu.
“ATMIS forces are currently assessing the security situation,” the AU force, known as the African Union Transition Mission in Somalia (ATMIS), said in a statement, without giving further details.
Islamists claim they killed 137 troops
Al-Shabab claimed in a statement that it carried out suicide bomb attacks and killed 137 soldiers.
A Somali military captain told Reuters news agency that the militants attacked two bases, which he said “prompted a fierce battle for hours. All groups, including al-Shabab, suffered heavy casualties.”
Another military commander told Agence France-Presse that the attack began when “a suicide bomber drove a vehicle with explosives targeting the ATMIS base.”
“The terrorists were forced to retreat and flee,” Commander Mohamed Yerow Hassan said, adding that the “situation is back to normal now.”
Local residents said they woke up to the sound of huge explosions and heavy weapons.
“Now we see al-Shabab in the town. We cannot know how many died. We are not hearing any shots from ATMIS and government now,” local resident Rukia Farah said.
The al-Qaida-linked jihadist group seeks to establish its own rule based on its strict interpretation of Islamic law in the fragile Horn of Africa country.
Somali government on the offensive
In recent months, the army and militias have retaken swathes of territory in the centre of the troubled country in an operation backed by ATMIS and US airstrikes.
The 20,000-strong ATMIS force has a more offensive remit than its predecessor known as AMISOM.
Its goal is to hand over security responsibilities to Somalia’s army and police by 2024.
Despite the gains by ATMIS and other pro-government forces, the militants have continued to strike with lethal force against civilian and military targets.
In the deadliest al-Shabab attack since the offensive was launched last year, 121 people were killed in October by two car bombings at the Education Ministry in Mogadishu.
United Nations chief Antonio Guterres said in February that 2022 was the deadliest year for civilians in Somalia since 2017, largely as a result of al-Shabab attacks.