The Somali capital, Mogadishu, has been hit by some of the fiercest fighting in the city in months, in what is seen as a major setback for the government, BBC reports.

The clashes began shortly after dawn between Islamist al-Shabab militants and government forces, backed by African Union (AU) troops.

The AU forces are reported to have used tanks and heavy artillery.

Al-Shabab withdrew from Mogadishu in August and the government then declared that the city was under its control.

The fighting occurred in the northern districts of Karan and Huriwa on Thursday.

There are reports of casualties but the details are not yet known.

It followed an attack by al-Shabab on Wednesday on a military training camp run by AU troops in Wadajir to the south of Mogadishu.

That area had previously been considered relatively safe.

Since the Islamists made their "tactical withdrawal" from Mogadishu, there have been several suicide attacks in the city.

The most recent happened on Tuesday in the Hodan district - at least five people were killed.

Earlier this week al-Shabab announced that it was changing its name to Imaarah Islamiya.

The BBC's East Africa Correspondent, Will Ross, says the move may have been designed to send a message to the international community that al-Shabab is not on the verge of defeat.

The African Union has about 9,000 troops in Mogadishu to prevent the internationally-backed government from being overthrown.

Kenya also sent its soldiers into the south of Somalia in October, following a series of cross-border kidnappings which it blamed on al-Shabab.

The Kenyan parliament on Wednesday agreed to integrate its troops in Somalia into the AU force.

Somalia has endured more than two decades of war and for much of that time had no functioning government.

Some parts of the country have been hit by a severe drought this year.