21:17 GMT, July 5, 2009 Heavy shelling between Somali rebels and government forces near the Presidential palace in Mogadishu killed at least twelve people on Sunday, witnesses said, and the Prime Minister looked for help from more African Union peacekeepers.

Prime Minister Omar Abdirashid Ali Sharmarke said more AU troops were expected soon to back his forces but gave no further details on Sunday.

The government and rebels who want to install an Islamic state in the east African country blamed each other for instigating the violence.

More than 4,000 African Union peacekeepers are in Mogadishu, but they come under regular attack and are generally confined to protecting government installations.

"It was a very gruesome scene," said Sahra Abdulle, a Mogadishu resident who saw bodies in the streets on Sunday and wounded people running from the mortar shells.

Another witness, Suleyman Abdulkadir, said at least 12 people died.

A surge of violence started in May in Mogadishu, killing about 200 people and forcing tens of thousands to flee the capital.

Somalia has not had an effective government since 1991 when the overthrow of a dictatorship plunged the country into chaos.

Besides frequent land battles, the power vacuum has also allowed pirates to operate freely around Somalia's 3,060-kilometre coastline.

Many fear the lawlessness will allow terrorists to gain a toehold in the Horn of Africa.