At least 40 people civilians have been killed and 150 others injured in heavy shelling and gun fire exchanged between Somali government troops and rebel fighters in Somalia's capital Mogadishu since Tuesday, Radio Garowe reports.

Somali government troops backed by African Union peacekeepers came under coordinated attacks from rebel fighters in northern districts Hodan, Hawlwadag and Bondhere, on Tuesday while other parts of the restive capital received share of the indiscriminate shelling.

The clashes started on Monday after militant fighters from Al-Shabaab launched attacks on the pro-government forces.

"At least 26 civilians were killed when mortar shells smashed parts of Bakara market. Bitter shelling also that rocked other parts of the city," said Ali Muse, the head of Mogadishu Ambulance Services.

12 others were reportedly killed in other parts as warring sides exchange heavy gunfire.

He added that more than 150 civilians were wounded in the Monday's and Tuesday's clashes. The fighting is still going on in parts of capital, he stated.

Reports suggested that Armored Tanks belonging to African Union troops have been seen patrolling the streets of Mogadishu.

Al-Shabaab, a powerful insurgent group has declared an all out war against the UN-backed government, urging people to take cover.

"We are embarking on a large scale offensive against the apostate government and its foreign backers, so we urge people to dig holes inside their homes to avert possible civilian casualties," said Sheikh Ali Mohamud Dhere, Al-Shabaab spokesman.

Both the government and the insurgents have vowed to continue with the battle as

Civilians bear the brunt of ceaseless misery.

The restive seaside capital has been wrecked by deadly clashes between rebel fighters and government troops backed by AU troops in recent past.

Powerful militant groups are bent on overthrowing fragile UN-backed transition government, which controls little more than a few blocks of Mogadishu.