(CNN) -- Bodies littered the streets of the third largest city in Somalia on Friday after Islamic fighters took control of the city, residents said.
Fighters from the armed Islamic group Al Shabab took control of Kismayo, a port city in southern Somalia, after fighting between tribal militias. Kismayo is 300 miles southwest of Somalia's capital of Mogadishu.
Halimo Mohamed Hassan, a mother in Kismayo's Alaney neighborhood, said six bodies were in front of her house.
"From 9 a.m. this morning, the fighting has intensified, with both sides using a lot of heavy guns including anti-aircraft guns," she said. "My children and I took cover under our beds and we stayed for three hours, till the situation subsided."
Hassan said heavily-armed Islamist militias remained on the streets, and the rival clan militia are rumored to have left the city in defeat.
"There is (a) very harsh humanitarian crisis in the city," said Ali Bashi Abdullahi Igal, head of Fanole human rights group. "The fighting has displaced more than 5,500 people from the city."
Fifteen civilians were killed on Friday, he said, including a mother and her two children, ages 3 and 5, who were crushed in their house when it collapsed under heavy anti-aircraft fire.
More than 70 people were killed and 168 wounded in three days of heavy fighting between Al Shabab and tribal militias.
"We are condemning this inhumane acts of violence," Igal said. "Both sides have breached the international laws."
There is a lack of medical care for the wounded, with only one doctor and two nurses at the city's only operational hospital, he said. Civilians are "suffering at the hospital," Igal said.