(CNN) -- Militants in Somalia's capital city killed at least 20 people and wounded dozens of others, the director of a local ambulance group in the capital said Monday.
Radio Shabelle in the capital, Mogadishu, reported the death toll at 30.
The fighting broke out between Al-Shabaab fighters and Somali government forces backed by African Union forces after Al-Shabaab spokesman Ali Mahamoud Rage called for members of the rebel group to fight, said the ambulance director, Ali Musa.
The fighting, which was marked by an exchange of artillery fire, erupted soon after Al-Shabaab spokesman Ali dhere declared what he called the final phase of the group's war against "invaders" -- a reference to African Union troops who are propping up the transitional government of Somalia.
"We are launching a final war to terminate the invading infidels in Mogadishu and all forces from the Islamic provinces are going to take part and we will wipe out the enemies out of Mogadishu " said Ali dhere.
He further warned that his group would not cease fighting until unless they expel forces from the African Union Mission to Somalia.
"We can confirm that at least 20 people have been killed and 53 others were wounded," said Ali Musa. He predicted that the casualty figures would rise, "as we are still busy collecting the dead and the wounded."
Separately, Madina Hospital in south Mogadishu said it had received 100 people wounded in Monday's fighting.
Al-Shabaab controls most of southern Somalia.