There's been heavy fighting in the Somali capital, Mogadishu.
At least 15 people have been killed and 90 wounded.
Correspondents say the fighting is the heaviest since Ethiopian troops withdrew from the city in January after a new president was elected.
The BBC reports the battle focused on the south of the city where rebels fired mortars at the presidential palace. A base for African Union and government troops was also targetted.
Somalia has not had a functioning national government since 1991.
An AU force of 3400 peacekeepers from Burundi and Uganda has been deployed in the capital since 2007.
Eleven peacekeepers from Burundi were killed in a suicide attack on Sunday at a barracks in Mogadishu.
Burundi has vowed to send more peacekeepers to the AU mission.
Defence Minister Lt Gen Germain Niyoyankana told Radio France Internationale a battalion of 850 men would be sent as reinforcements as soon as possible.