Somalia's government called on Monday for the lifting of an arms embargo to help it resist an Al-Qaeda-backed Islamist insurgency.

The appeal follows Al-Qaeda's declaration last week that the Somali militant group Al-Shabaab was joining its ranks, which raised concerns the Somali rebels' weakened campaign might be re-energised.

Security experts speculate Al-Shabaab might be encouraged to carry out an Al-Qaeda-style attack, perhaps on neighbouring Kenya which has sent troops to Somalia fight the Islamist insurgency.

Urging foreign powers to help, Mogadishu asked the international community to "lift the arms embargo on Somalia so that it could defend the country" and "increase and reinforce the Somali National Army".

"We ... believe that their union will increase the insecurity in Somalia, east Africa and the rest of the world and that Somalia risks becoming an al Qaeda base in east Africa," Somalia's information ministry said in a statement.

The United Nations imposed the arms embargo in 1992, the year after clan warlords overthrew dictator Siad Barre and plunged the country into a civil conflict that still festers.

The embargo has been amended several times, including in 2006 to allow for an African peacekeeping force to prop up the government and in 2007, in part to allow for the peacekeepers to be supplied with weapons and military equipment.

The request comes ahead of a conference in London next week to discuss measures to tackle instability in Somalia and piracy off its shores.

"The Somali government wants to buy its own tanks and modern weapons to crush Al-Shabaab," government spokesman Abdirahman Osman told Reuters.

Al-Shabaab, which professed loyalty to Al-Qaeda several years ago, relinquished control of the coastal capital in August, under pressure from the African Union's AMISOM force.

The rebels continue to hold swathes of central and southern Somalia but are being squeezed out of some areas by Kenyan and Ethiopian troops.

Al-Shabaab spokesman Sheikh Ali Mohamud Rage led a rally in support of Al-Qaeda in the rebel-controlled town of Elasha, 15 km (10 miles) outside the capital, on Monday.

"Let Somali participants not waste time at the London conference. They intend to colonise Somalia," he told hundreds of residents from the town.

Some residents said they had been forced to take to the streets. One said the militants had driven through Elasha on Sunday in cars mounted with loud speakers ordering business owners to close their doors on Monday or face punishment.

"We hate Al-Shabaab, how can we love Al-Qaeda," said one mother-of-six, declining to be named in fear of a reprisal attack.

Somalia is a hotspot in the US-led was on militant Islam and the Al-Qaeda-Al-Shabaab merger appeared a calculated bid to restore morale and reinforce each other's relevance after testing periods for both.

"The (Al-Qaeda) announcement seems to suggest that the Al-Qaeda core is looking to cement its relationship with jihadi affiliates outside of South Asia and shows how East Africa is moving to the centre of global security concerns," said Robert Crowley of Janusian risk consultants.

Britain has warned it is only a matter of time before Islamist militants trained in Somalia strike on British soil.