African Union and Somali government forces are attempting to seize a militant stronghold outside Mogadishu.

The operation launched Tuesday near Somali capital targets the al-Shabab-controlled town of Afgoye, site of a massive camp for internally displaced Somalis.

Witnesses reported heavy fighting between the two sides.

An African Union statement described the offensive as a “carefully planned operation” to bring security and stability to people in the Afogye corridor.

The area is home to about 400,000 Somalis driven from their homes by drought and years of war. The AU Mission in Somalia said al-Shabab has been preventing aid agencies from operating in Afgoye.

The AU force commander, Lieutenant General Andrew Guttie, said the troops are taking “every precaution to prevent harm and injury to civilians,” and will only fight if attacked by al-Shabab militants.

VOA's Somali Service reports the Somali and AU troops launched an attack Tuesday on a road east of Afgoye. The also moved in on the town from the north, moving along a main road that links Afogye to the town of Bal'ad.

The African Union says its forces have been careful to avoid built-up areas and are making good progress toward Afogye.

Al-Shabab has been fighting to overthrow Somalia's U.N.-backed transitional government and impose strict Islamic law.

The group once controlled most of southern and central Somalia but has steadily lost ground in the past 18 months to AU, Somali, Kenyan and Ethiopian forces.