Islamist militiamen control large swathes of territory in Somalia
At least five Somali policemen have been killed in a roadside bomb blast in the capital, Mogadishu.
The officers were driving near a road junction in the south of the city when their vehicle was blown up.
Meanwhile, pro-government forces have regained control of a police station which had been overrun by Islamist insurgents, witnesses say.
At least three people were killed in the fighting in the Yaqshid area, which was seized by Islamists a month ago.
A government member of parliament, Salad Ali Jelle, was quoted by the AP news agency as saying there was fighting during the night.
But, he said, the rebels were forced to flee the area about 0800 local time (0500 GMT) and pro-government forces were now in control.
At least 60,000 people have fled the recent fighting around Mogadishu, which has left at least 200 people dead.
The internationally-recognised government only controls parts of Mogadishu and other pieces of territory.
Islamist radicals control much of southern Somalia.
The BBC's Mohammed Olad Hassan in Mogadishu says the loss of the police base means it will be harder for the Islamists to defend other parts of north Mogadishu.
The latest fighting comes after President Sheikh Sharif Sheikh Ahmed ordered a fight-back against al-Shabab guerrillas.
He says the group, accused of having links to al-Qaeda, has in its ranks foreigners who have fought in Iraq and Afghanistan.
Mr Ahmed, a moderate Islamist, was elected by a unity government in January as part of a UN-backed peace initiative.
Hardline Islamist groups want to impose a stricter version of Islamic law and are demanding the departure from Somalia of the 4,300-strong African Union peacekeeping force.
Somalia has not had a functioning national government since 1991, and years of fighting have left some three million people - a third of the population - needing food aid.