Somali forces backed by African Union troops have begun an operation against al-Shabab rebels in northern Mogadishu, as the U.N.-supported coalition aims to continue recent advances against the al-Qaida-linked insurgent group.

The African Union Mission in Somalia said the operation launched early Friday is meant to clear al-Shabab fighters from the northern fringes of the Somali capital, from where the militants have been able to stage several recent attacks.

The move comes two weeks after AMISOM troops delivered a major defeat to al-Shabab, forcing the fighters out of Baidoa, the country's third largest city, which was considered an important rebel stronghold.

Al-Shabab still controls much of southern and central Somalia, but has been steadily losing ground to offensives by Ethiopian, Kenyan and African Union troops.

The group was driven out of Mogadishu by government and African Union forces last year but has continued to carry out sporadic, guerilla-style attacks in the city.

Al-Shabab is fighting Somalia's weak transitional government in an attempt to impose its strict version of Islamic law on the country.

Last month, al-Qaida announced a formal alliance with al-Shabab, though the groups are thought to have had informal ties for several years.