Al Shabaab launches first attack since founder killed by U.S.

MOGADISHU, Somalia - At least 12 civilians were killed Monday in a suicide bombing that targeted African Union troops in Somalia's Lower Shabelle region, an official said Monday.

Abdiqadir Mohamed Nor, the governor of Lower Shabelle, told The Associated Press that the attack happened near the Elasha Biyaha settlement.

Somali police official Hassan Ali said a suicide bomber detonated his explosives-laden car next to a convoy of African Union forces moving near two minibuses.

He said the death toll may rise, as it remained unclear if there were any casualties among the African Union troops who are in the area to oust militants from their last strongholds.

This is the first serious assault by suspected Islamic extremists since the leader of Somalia's al Qaeda affiliate was killed in a U.S. airstrike last week.

Somali officials warned over the weekend that there is a probability of attacks following the killing of al Shabaab leader Ahmed Abdi Godane by a U.S. airstrike last week.

Gen. Khalif Ahmed Ereg, Somalia's national security minister, said on Friday likely targets include medical and educational institutions. Ereg said the government is vigilant and prepared its armed forces to prevent such attacks.

Two security experts told CBS News the leadership upheaval could bring al-Shabaab to break away from al Qaeda and instead pledge allegiance to the Islamic State group in Syria and Iraq.

The U.S. has carried out several airstrikes in Somalia recent years.

A U.S. missile strike in January killed a high-ranking intelligence officer for al-Shabaab, and last October a vehicle carrying senior members of the group was hit in a U.S. strike that killed al-Shabaab's top explosives expert.

Al-Shabaab gained international notoriety a year ago this month when it attacked the upscale Westgate Mall in Nairobi, Kenya, killing at least 67 people. The U.S. strike last week targeted Godane and other planners of the bloody assault on the mall, officials said.