Twenty people were killed and 51 others wounded on Wednesday in heavy clashes between Somali government forces backed by African Union (AU) peacekeeping troops and Islamist fighters over the control of key locations in Mogadishu, a medical official said.

The fighting broke out after AU peacekeeping forces fanned out into the insurgent-held side of the Somali capital, where fierce clashes ensued between radical Islamist fighters and the peacekeepers.

"Twenty people all of them civilians were killed and 51 others wounded in Mogadishu after they were caught in the fighting," Ali Muse, head of the local emergency service, told Xinhua.

The Somali government said its forces supported by AU peacekeepers took over three strategic locations from the Islamist insurgency in an early morning offensive on the rebel held side of the divided Somali capital.

Islamist commanders from the Al Shabaab group said they repulsed the government onslaught against their positions in the south of the capital, claiming that they have killed several AU and government forces and taken some alive.

Somali government officials said they had killed a number of insurgents including some foreign fighters supporting the rebels.

Clashes between the government forces and the Islamist group were also reported in a number of regions along the Somali border with Kenya and Ethiopia.

Residents in Hiran and Gedo regions, in the center and south of the Horn of African country respectively, were reported to have fled their homes amid exchanges of heavy artillery bombardment. The battle zone was lately run by Al Shabaab.

It is now clear who has taken control of the contested areas in the south and center of the war-torn country, with reports saying neither is in full control.

The clashes erupted following days of relative calm. Prior to the latest fight, at least 30 people had been killed and 50 others injured in a suicide car bomb attack against government forces.

Some observers see the current advances by AU troops as a significant step taken against insurgents, who are suffering a major setback after a streak of successes against government forces.