Deadly street battles broke out Friday after insurgents fired mortars at an African Union cargo plane, making good on a threat to attack any aircraft using the capital's main airport, officials said.

The aircraft landed safely and was not hit, said Eydurus Sheik, an immigration officer. But within hours, the capital was rocked by violence as government forces battled the Islamic militants, witnesses said.

At least seven civilians were killed, according to Mogadishu resident Said Nur Farah, whose brother was among the dead.

"We collected his body from under a tree," Farah said. "He had been talking to friends when the shell landed."

The violence comes days after Islamic insurgents who want to topple the government vowed to attack any planes using Mogadishu's international airport. The Islamic group objects to the airport being used by troops from Ethiopia and the African Union, which it accuses of propping up the fragile government.

"These mortars will not deter us from doing our job," Barigye Bahoku, a spokesman for the African Union peacekeeping force in the capital, told The Associated Press. He said the shells landed outside the airport's walls.

The AU has about 2,000 peacekeepers in Somalia, far fewer than the 8,000 planned. The troops are mostly based at the airport due to the daily violence in the capital.

One of the most violent and impoverished nations in the world, Somalia has not had an effective central government since 1991. The insurgency has killed thousands of civilians since early 2007.

Islamic militants with ties to Al Qaeda have been fighting the government and its Ethiopian allies for control since their combined forces pushed the Islamists from the capital in December 2006. But the government has failed to deliver any basic services, is riddled with corruption and comes under daily attack.