Mogadishu - The death toll of the heaviest fighting in the Somali capital Mogadishu this year has risen to over 50 as Islamist insurgents, backed by foreign fighters, continue to battle pro-government militia, local media reports said Monday.

Radio Garowe said that insurgent groups al-Shabaab and Hizbul Islam had over the last few days gained ground from the Islamic Courts Union (ICU), a militia that is now supporting the new moderate Islamic regime.

At least 15 people were killed in one attack, when a shell hit a mosque. Other civilians died as their apartments were hit by bullets and grenades.

Somalia's transitional government only controls parts of Mogadishu and can ill afford to lose more ground to the insurgents, who have refused to lay down arms, saying that new president Sheikh Sharif Sheikh Ahmed is too close to the West.

Sheikh Sharif, who led the ICU when it controlled Mogadishu in 2006 and worked alongside many of those who are now insurgents, came to power earlier this year as part of a western-backed peace process.

Somali Security Minister Omar Hashi said that foreign fighters took part in the attacks and vowed to beat back the insurgents.

Foreign diplomats believe there are around several hundred foreign fighters in Somalia and that more are entering the country, either to fight for al-Shabaab or seek a safe haven in the chaotic Horn of Africa nation.

The US believes that al-Shabaab has close links to al-Qaeda.

Reports last Thursday said that the insurgent groups were funnelling large amounts of heavy weaponry into Mogadishu in preparation for a major attack.

The Somali government has accused Eritrea of providing the weapons to the insurgent groups.

The insurgency has claimed the lives of around 16,000 people, mainly civilians, since early 2007, and the resultant insecurity has helped feed an explosion of piracy in the Gulf of Aden.

An AU peacekeeping force, comprised of troops from Burundi and Uganda, is on the ground but is hopelessly undermanned, with only 3,500 troops in active service compared to the planned 8,000.

It has been propping up the government alone since Ethiopia pulled out is forces, who had been there independently of the peacekeepers, in January.

Somalia has been embroiled in chaos since the 1991 ouster of dictator Mohamed Siad Barre, and is widely regarded as a failed state. (dpa)