African Union (AU) forces have launched a beach assault and taken control of parts of Kismayo, the last major stronghold in Somalia held by Islamist militants, Kenya's military says.

The port city has been a bastion of the al-Qaeda-aligned group al-Shabab.

The Kenyan troops are part of the AU's Amisom force, which is trying to wrest control of the country for the newly elected UN-backed president. Kenyan military spokesman Col Cyrus Oguna confirmed that parts of Kismayo had been captured and the rest was expected to fall soon.

Al-Shabab spokesmen said fierce clashes were taking place, BBC News reported.