Somali troops backed by African Union forces have launched an assault to retake the al-Shabab stronghold of Barawe, key to the financing of al-Shabab fighters.

Al Jazeera's Catherine Soi, embedded with the African Union Mission in Somalia (AMISOM) in Barawe, said "some al-Shabab fighters were fleeing the battle, taking boats and heading out to sea, while others were melting in to civilian areas."

Brigadier General Dick Olum, from AMISOM told Al Jazeera on Sunday that Barawe "was hours away from being taken".

"Barawe has one the biggest ports in Somalia, and taking the town will be a huge boost for the Somali government and AMISOM forces."

Al-Shabab reportedly charged taxes to ships that sailed or docked from Barawe's port, raising revenues to expand its military campaign. 

The AU says al-Shabab uses the town as a base to launch attacks on Mogadishu. Barawe has been held by the al-Qaeda-linked fighters for six years.

On Saturday, al-Shabab commander Mohamed Abu Abdallah vowed that the fighters would maintain pressure on Somali and AU forces even if they took Barawe.

Al-Shabab is fighting to topple Somalia's internationally-backed government, and regularly launches attacks against state targets, as well as in neighbouring countries that contribute to the AMISOM force.

The 22,000-strong AMISOM force, with soldiers drawn from six nations, have been fighting alongside government troops against al-Shabab since 2007.

Source: Al Jazeera and agencies