MOGADISHU: Somalia's Islamist fighters retook the key southern town of Hudur on Sunday, residents and the militants said, in the first territorial fight-back by the Al-Qaeda-linked Shebab for several months.

Heavily armed Shebab fighters swept into the regional capital of the Bakool region early on Sunday, taking the town peacefully just hours after Ethiopian troops who had held it since late 2011 left, said resident Hussein Madker.

"Hudur is now under the control of the Shebab fighters again after the Ethiopian soldiers moved out late last night," Madker said.

The Ethiopian troops left the town late Saturday with their heavy weaponry, alongside allied Somali forces and residents who feared what would happen after their pull-out, locals said.

"The city is now firmly in the hands of the mujahedeen," the Shebab said in a message on their Twitter account, boasting of how the "Ethiopian invaders fled the city".

The recapture of Hudur marks a sharp turnaround for the Shebab, who have lost a string of towns in recent months to the 17,000-strong African Union force, which fights alongside Somali government forces.

However, it was not immediately clear whether Ethiopian forces had pulled out due to pressure by the Shebab, or for how long the Islamists intended to hold the town.

"The Somali government troops also went along with the Ethiopian soldiers, as well as some civilians who feared for their lives", said resident Hudow Mohamed.

Hudur lies some 180 kilometres (110 miles) west of the Ethiopia's main base in Somalia, the city of Baidoa.

Ethiopian troops crossed the border into southwestern Somalia in late 2011 to attack Shebab bases, shortly after Kenyan troops invaded Somalia from the far south.

While Kenyan troops have since joined the AU force, Ethiopian troops have remained separate.

Somali military commanders in Baidoa confirmed the Shebab had taken Hudur but would not give further details.

Despite recent losses the Shebab remain a potent threat, still controlling rural areas as well as carrying out guerrilla attacks in areas apparently under government control.

Some, retreating ahead of AU-led assaults, have relocated to the northern Golis mountains in Somalia's semi-autonomous Puntland region.

Somalia has been ravaged by conflict since 1991 but a new UN-backed government took power in September, ending eight years of transitional rule by a corruption-riddled administration.

Many have said the new government offers the most serious hope for stability since the fall of dictator Mohamed Siad Barre in 1991.