An extremist leader vowed to avenge the civilian deaths and threatened retaliatory attacks in two African countries that supply troops to the African Union peacekeeping mission stationed in Mogadishu.

The president was unhurt and his plane took off safely, police said, but the deaths of civilians are fueling a growing anger toward AU peacekeeping forces that are stationed in Mogadishu to help protect the U.N.-backed government.

Somalia's capital sees near-daily bloodshed as a powerful insurgent group with links to al-Qaeda tries to overthrow the fragile government and push out about 5,000 AU peacekeepers. Both sides have been accused of indiscriminate shelling.

At least 20 bodies, most of them civilians, lay in the streets after yesterday's fighting, said Ali Muse, the head of Mogadishu's ambulance service. Four people later died at the hospital. Muse said that about 60 people were wounded as mortar rounds slammed into residential areas.

"Soldiers from Uganda and Burundi are our enemy. They often massacre our people. We will not let them go unpunished but will target them in Kampala and Bujumbura," the capitals of the two countries, said Sheikh Ali Mohamed Hussein, a leader of al-Shabab, the extremist group linked to al-Qaeda that controls much of southern Somalia.

The shelling started soon after insurgents fired toward President Sheik Sharif Sheik Ahmed's plane, said police spokesman Abdullahi Hassan Barise.

Yesterday's violence - deadlier than many recent clashes in this once-beautiful seaside city - followed a pattern that witnesses say is becoming all too common. First, insurgents fire at government or AU targets. Then those forces respond by shelling insurgent bases, most of which lie in residential areas.

The result is that most of those killed in Somalia's war are civilians.