MOGADISHU - Somalia's al Shabaab Islamist fighters attacked government positions near the president's palace in a third day of fighting as the death toll hit 60, residents and a human rights group said on Friday.

Witnesses said government forces backed by African Union troops launched a barrage of artillery fire to repel the al Qaeda-linked fighters.

Meanwhile, the government also called for a probe into all non-governmental organisations operating in the country after a report by the United Nations' Somalia Monitoring Group said aid was being diverted to insurgents.

The Elman rights group said six civilians died and 23 were injured as the clashes shifted to the Bakara market from where the rebels had launched their attack.

At least 54 people were killed in the first two days of fighting as rebels tried to destabilise the government before a long-awaited offensive aimed at driving the insurgents out of Mogadishu.

Somalia has lacked an effective central government for 19 years and Western and neighbouring countries say the country provides sanctuary for militants intent on launching attacks in east Africa and beyond.