African Union troops in Somalia killed at least 30 al-Shabab fighters as they repulsed an attack by the armed group on their base, the AU mission said.

Heavily armed al-Shabab fighters attacked the base belonging to the African Union Mission in Somalia (AMISOM) early on Sunday, blowing up two vehicles and engaging the African troops in a gun battle that lasted several hours.

"The militants were dealt a heavy blow, with at least 30 of them put out of action, following intense fighting," AMISOM said in a statement on Monday.

"Eight vehicles which ferried the terrorists, including two Vehicle Borne Improvised Explosive Devices were Destroyed and an assortment of weapons recovered," the statement said.

AMISOM said it lost four soldiers in the attack and six others were wounded.

Contradicting the AMISOM claims, al-Shabab's military operations spokesperson Abdiaziz Abu Mus'ab told Al Jazeera on Sunday that the group lost only 14 fighters and killed dozens of African Union soldiers.

"The Mujahideen fighters entered the crusaders' base and killed at least 59 of them. Our fighters also attacked five other bases," Mus'ab said.

Also on Sunday, three air attacks targeted areas in south and central Somalia under the control of the al-Qaeda linked group.

In El Buur an air attack targeted a vehicle carrying five people including a mother and a child, according to residents. In another attack near the port city of Kismayo a vehicle was targeted leaving at least three people dead, all civilians according to a local member of parliament.

No one has taken responsibility for the air attacks but they come days after the White House granted its military broader authority to carry out attacks in Somalia against al-Shabab fighters.

"The additional support provided by this authority will help deny al-Shabab safe havens from which it could attack US citizens or US interests in the region," Pentagon spokesperson Captain Jeff Davis said in a statement on Friday.

Two US defence officials, speaking on the condition of anonymity to Reuters news agency, said parts of Somalia had been declared an "area of active hostilities" for at least 180 days by the White House on Wednesday. The capital of Mogadishu was not included.

Since President Donald Trump came to office in January 2017, 38 US air attacks have taken place in Somalia killing 13 civilians, according to The Bureau of Investigative Journalism (TBIJ).

In Obama's last year in office, the US carried out 15 air attacks in Somalia killing five civilians, according to TBIJ.