By Abdi Sheikh and Feisal Omar

MOGADISHU, April 19 (Reuters) - Islamist al Shabaab militants attacked an African Union peacekeepers' convoy on Sunday in southern Somalia, wounding at least three people and burning two vehicles, a Somali army officer said.

Al Shabaab said it had launched the attack near the town of Leego, in the southern Lower Shabelle region, and that it had destroyed two vehicles and had killed five members of the force.

The militant group, which wants to topple the Western-backed government and impose its strict interpretation of Islam on Somalia, has been driven out of major strongholds by African and Somali forces but continues to harass them and launch bomb and gun attacks against officials, politicians and others.

The African Union Mission to Somalia (AMISOM) could not be reached for immediate comment.

Dozens of well-armed fighters attacked the AU convoy, prompting an exchange of heavy fire, residents said.

Colonel Aden Mohamed, a senior Somali military officer, told Reuters from Leego that he had seen at least three AMISOM soldiers wounded and two burned vehicles. He said the casualty figure could be higher.

Sheikh Abdiasis Abu Musab, al Shabaab's military operations spokesman, told Reuters of the five dead and the two destroyed vehicles.

The group often cites higher death tolls or casualty figures than numbers given by officials.

Last week al Qaeda-aligned al Shabaab militants stormed a government building housing two ministries in the heart of Mogadishu, killing at least 10 people.

(Writing by Edmund Blair; Editing by David Goodman)