MOGADISHU, Somalia (AP) -- At least 12 civilians were killed Monday in a suicide attack targeting African Union troops in Somalia's Lower Shabelle region, the first serious assault by suspected Islamic extremists after the killing of al-Shabab's top leader in a U.S. airstrike last week, the police and a regional official said.
The attack happened near the Elasha Biyaha settlement, said Abdiqadir Mohamed Nor, the governor of Lower Shabelle.
A suicide bomber detonated his explosives-laden car next to a convoy of African Union forces moving near two minibuses, said Somali police official Hassan Ali. Then, amid the confusion, another bomb went off when a second suicide attacker rammed his car into a convoy escorting Abdifatah Shaweye, the Mogadishu intelligence commander, who was in the area to inspect the scene of the first blast. Shaweye suffered "slight wounds" and was rushed to a Mogadishu hospital. There were no fatalities from the second blast, Ali said.
Two soldiers were wounded in the attack described as a "heartless massacre" by Ali Aden Houmed, spokesman for African Union forces in Somalia.
Al-Shabab claimed responsibility for the attack in a radio broadcast.
Somalia's government warned over the weekend that there is a probability of attacks following the killing of Ahmed Abdi Godane, who was confirmed dead by the U.S. on Friday following a Monday airstrike.
Possible targets include medical and educational institutions, said Gen. Khalif Ahmed Ereg, Somalia's national security minister, in a televised speech on Friday.
Mortar shells struck a Mogadishu neighborhood on Sunday, the day after al-Shabab named a new leader and vowed to avenge the death of Godane.
Al-Shabab said in a statement over the weekend that it remains aligned with al-Qaida, according to the SITE Intelligence Group, which monitors statements by Islamic militant groups.
"Avenging the death of our scholars and leaders is a binding obligation on our shoulders that we will never relinquish nor forget no matter how long it takes," said the al-Shabab statement, according to SITE.
Godane, who was also known as Mukhtar Abu Zubeyr, was al-Shabab's spiritual leader, and the U.S. had offered a reward of up to $7 million for information leading to his arrest.
Godane had publicly claimed al-Shabab was responsible for an attack on a mall in the Kenyan capital, Nairobi, in which 67 people were killed a year ago. Kenya later became part of the African Union force that is bolstering Somalia's weak, U.N.-backed government against al-Shabab's insurgency.
Backed by African Union forces, Somali government troops recently launched a military offensive aimed at ousting al-Shabab militants from their last strongholds in southern Somalia, including the coastal city of Barawe, where military officials say al-Shabab plots attacks across Somalia. Scores of people have been killed this year, including lawmakers who are being targeted for assassination.
Ugandan Brig. Dick Olum, a commander of African Union troops fighting al-Shabab, said the death of Godane left them motivated to escalate the fight against the militants.
"It means that now they are off balance," he said, referring to Islamic extremist militants. "It's time to put them on pressure, to escalate. We have to go and take over Barawe before the militants sit down and make a plan."
The U.S. State Department declared al-Shabab a terrorist organization in February 2008.
Associated Press reporter Rodney Muhumuza in Kampala, Uganda, contributed to this report.