Heavy fighting between government forces and militant Islamists in Somalia's capital, Mogadishu, has forced the closure of a hospital, an aid group says.Dr Ahmed Mohamed said the shelling of a maternity unit run by SOS Children on Monday killed one staff member and forced patients and staff to flee.This was the first time in 25 years that the hospital had closed, he said.Government forces are fighting the Islamist group al-Shabab in Somalia.They are backed by 9,000 African Union (AU) troops.On Monday, the AU said they have driven al-Shabab militants out of their last stronghold in the north of Mogadishu."It has been a big achievement to remove [al-Shabab] from the city, and put an end to the fighting that disrupted so many lives," AU force spokesman Lt Col Paddy Ankunda said.Al-Shabab still has a presence in the outlying district of Daynile, a BBC reporter in Mogadishu says. It also controls many southern and central areas.Dr Mohamed told the BBC that 40 women in the maternity unity had to flee, including women who had given birth by caesarean section.Children being treated for severe malnutrition also fled and he feared some of them may have died, he said.He appealed to the AU-backed government forces and militants to leave the area."I am pleading and I am begging both parties... to leave the place and allow people to come back and get the assistance from the hospital," Dr Mohamed said.Somalia is the country worst hit by the Horn of Africa's worst drought in 60 years - many thousands of people have flocked to Mogadishu in recent months to get food aid despite the danger.Al-Shabab said it carried out a bomb attack in Mogadishu last week which killed more than 80 people.In August, it said it had made a tactical withdrawal from Mogadishu following a sustained offensive by AU forces.Since then, it has increasingly relied on guerrilla tactics to fight the weak interim government, analysts say.Somalia has been without a functioning central government since the Siad Barre regime fell in 1991.