Somali government and African Union forces have seized two of the militant group al-Shabab's last strongholds in the capital, Mogadishu.

Witnesses told VOA's Somali Service that government troops captured two of the city's northern neighborhoods during a day of heavy fighting Monday.

Residents of the area reported hearing explosions and gunfire as government and AU soldiers advanced. A spokesman for the AU force said one AU soldier was killed in the fighting.

The offensive comes several days after al-Shabab suicide bombers killed at least 80 people at a Somali government compound.

It was al-Shabab's first major attack in the city since the group withdrew most of its fighters from Mogadishu in August. Since then the group had maintained control of a few scattered districts on the edge of the city.

Al-Shabab once controlled nearly all of Mogadishu but has steadily lost ground over the past year to AU and government forces.

The militants seek to topple the U.N.-backed transitional government and impose a strict form of Islamic law across Somalia.

The AU force, technically a peacekeeping mission, consists of about 9,000 soldiers from Uganda and Burundi.