African Union forces with Somali troops take control of Kismayo Islamist rebel city Somalia 2809122.

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.

Kenya sent its troops into Somalia last October after the fighters were blamed for a series of raids on Kenyan soil targeting its security forces as well as Western tourists.

Kenyan military spokesman Cyrus Oguna confirmed to the BBC that parts of Kismayo had been captured and the rest was expected to fall soon.

Mr Oguna said the joint operation of Kenyan Defence Forces and Somali government troops had begun at 02:00 local time (23:00 GMT Thursday) and was "basically amphibious".

Somalia has made progress in the past year in battling the group, who have wanted to impose their interpretation of Sharia law across the country since taking control of large swathes of south-central Somalia from 2007.

In June, Sheik Sharif Sheik Ahmed, the Somali president, named Western-educated Abdiweli Mohamed Ali as the nation's new prime minister. The Somali-American technocrat said he would make the re-establishment of security one of his top priorities.