A missile strike killed four Al-Qaeda allied Shebab rebels in war-torn southern Somalia, officials and witnesses said Friday, as the extremists are squeezed on three fronts by regional forces.

"An Al-Qaeda commander was targeted in Lower Shabelle early on Friday morning, a missile struck and destroyed his vehicle, killing him and several colleagues," said a Somali government official on condition of anonymity.

The missile strike 60 kilometres (37 miles) south of the Somali capital Mogadishu -- an area known as K60 -- was confirmed by local residents.

Residents said an aircraft fired a missile at a Land Cruiser with four passengers, reportedly including foreigners fighting with the Shebab.

Britain's security think tank, the Royal United Services Institution, estimates the total number of foreign fighters within the Shebab to be around 200.

Somali Prime Minister Abdiweli Mohamed Ali said Wednesday he would welcome Somalia's international allies to launch air strikes against the Shebab, who have been battling to topple his weak Western-backed government.

He called the Shebab a "global enemy, not only a Somali enemy".

The strike comes a day after international powers meeting in London pledged to boost efforts against instability in Somalia and vowed action against anyone obstructing the country's peace process.

"There was a missile strike near K60 this morning, the missile targeted a vehicle belonging to Al-Shebab," said Mohamed Ali, a resident in a nearby village.

"We are not sure who exactly was the target but four people apparently died and the vehicle was destroyed."

There were conflicting reports about the nationalities of those killed in the strike, and it was not immediately possible to establish their identities.

"We heard a very loud explosion, and people are saying the target was a vehicle of the Al-Shebab," said Ahmed Moalim, another resident.

Kenyan military, which has carried out air raids against the Shebab in southern Somalia, said they were not behind Friday's missile strike.

"That air strike is not from our end," Colonel Cyrus Oguna, a Kenyan army spokesman, told AFP.

In October, the United States acknowledged flying drones out of Ethiopia under a counter-terrorism campaign in the Horn of Africa but said the aircraft were unarmed and not carrying out raids.

Last month the hardline Shebab insurgents said a missile fired from a drone killed a fighter of Lebanese origin, about 13 kilometres south of Mogadishu.

The rebels on Wednesday lost control of their strategic base of Baidoa after truckloads of Ethiopian soldiers and pro-government Somali forces seized the town, the second major loss for the rebels in six months.

Baidoa was one of the Shebab's main bases and its capture leaves the group's fighters in central Somalia increasingly isolated, with African Union (AU) troops also chasing them out of the capital Mogadishu.

The Shebab, thought to number no more than 5,000 gunmen, are close to collapse, with reports that foreign fighters are fleeing to Yemen, the commander of the 10,000-strong AU force in Somalia said Thursday.

"In the last few days, close to 300 people, mainly foreign fighters, are streaming out of Somalia taking the direction of Yemen -- these are signs of defeat," said Ugandan Major General Fred Mugisha.