MOGADISHU, Somalia — At least 22 people have been killed and 80 wounded in heavy fighting between insurgents and government forces in the Somali capital Mogadishu, an official said Thursday.

“”These are the worst casualties we have seen for months,”” Ali Muse, head of Mogadishu’s ambulance service, told the German press agency dpa. “”Our staff are still collecting casualties, so the number (of killed and injured) could go up.””

Battles broke out between Islamist insurgents and African Union-backed government troops in north and south Mogadishu. Shells rained down on civilian districts as the two sides clashed.

Maj. Barigye Ba-Hoku, spokesman for the AU peacekeeping mission in Somalia known as AMISOM, told dpa that one Ugandan soldier had died and two were injured.

Two insurgents also were killed, he said.

AMISOM, which is made up of Ugandan and Burundian troops, is in the process of boosting its force to the mandated 8,000 soldiers.

Fighting has intensified over the past month as al-Shabab, a group with links to al-Qaida, and its allies push harder to topple the weak Western-backed government.

The government is penned into a few areas of Mogadishu by the militants, who control much of south and central Somalia.

More than 21,000 people have died in the insurgency, which began in early 2007.

The chaos-ridden Horn of Africa nation has been without an effective central government since 1991.