Members of al Shabaab, al Qaeda-linked insurgents, ride in their pick-up trucks after distributing relief to famine-stricken internally displaced people at Ala Yaasir camp 50km outside Somalia's capital Mogadishu.

Addis Ababa - World powers should take advantage of a retreat by Somalia's al Shabaab rebels and step up efforts to defeat them by backing government troops and imposing a no-fly zone and a sea blockade, the African Union said on Tuesday.

The al Qaeda-linked group pulled out of bases in Somalia's coastal capital Mogadishu at the end of August, raising hopes that its influence was waning in the Horn of Africa nation.

Al Shabaab warned it would fight on elsewhere but experts say it has been significantly weakened by internal divisions and a shortage of fighters.

“There's a shared belief by all of us that the time is now to make a difference in Somalia,” Ramtane Lamamra, Commissioner of the bloc's Peace and Security Council, told reporters.

“There can be some frustration that (AU peace keepers are) not fully equipped and that (government) troops are not fully operational so that they can take an immediate advantage at a period (when) al Shabaab are weaker than they used to be in the past,” he said in the AU's headquarters in Addis Ababa.

Somalia has not had an effective central government since the 1991 overthrow of dictator Mohamed Siad Barre. Al Shabaab has been waging a four-year insurgency against Western-backed government troops and AU peacekeepers.

The AU last year called on the U.N. Security Council to impose a no-fly zone and a maritime blockade on the war-shattered nation to cut the flow of arms and recruits to the rebels, but the world body has not carried out the request.

The United Nations will hold a meeting on Somalia in New York next week and Lamamra said he hoped “concrete steps” would be taken to support efforts to oust the rebels.

“We have been told that those recommendations are under consideration at UN level and we believe that the time has come now to implement those measures which are likely to change the dynamics of the situation in Somalia,” he said.

Somalia is in the grips of a famine that the United Nations says is killing hundreds daily. - Reuters