Three soldiers and two civilians have been killed in an Islamist attack on a Somali government base in southern Mogadishu, say residents.
Rocket-propelled grenades were launched at the base before both sides engaged in an hour of heavy clashes.
Two weeks ago, the Islamist-dominated opposition vowed “to liberate Somalia from the Ethiopian invaders”.
Meanwhile, the sacking of a minister over the weekend is leading to growing reports of a split in the government.
Since the Islamists were ousted by Ethiopian troops last year, hundreds have died in an insurgency.
The UN Secretary-General’s Special Representative for Somalia, Ahmedou Ould Abdallah, made his first visit in his new role to Mogadishu on Saturday.
He held talks with President Abdullahi Yusuf and Prime Minister Ali Mohammed Ghedi amid suggestions that a rift is growing between the two Somali leaders.
This comes as Somalia’s attorney-general and his deputy were sacked at the weekend.
It followed the arrest of the country’s chief justice on charges of corruption and abuse of power.
Attorney-General Abdullahi Dahir has refused to accept the decision, made by Somalia’s cabinet, saying only the president could sack him.
Mr Dahir is reported to have told a local radio station that any attempt to free the chief justice would be resisted by force.