A Somali police officer says at least five civilians have been killed in a suicide bombing that targeted African Union troops in the capital, Mogadishu.

Hassan Ali said Monday that 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.

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

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