African Union and Somali troops on Sunday took control of Barawe, a port town used by Al Shabab to bring in arms and fighters from abroad, after the Al Qaeda-linked militants fled without resistance, a Somali official said.
The African Union and the Somali military launched a joint offensive in March to drive the Islamist fighters out of towns and areas they control and stepped up their campaign in August after a surge in gun and bomb attacks in Mogadishu.
Al Shabaab members across Somalia have been arrested and smaller towns retaken, but the rebels still hold swathes of territory.
"I wish to share some very good news with the people of Somalia. Al Shabab terror capital Barawe is now under Somali government control," Lydia Wanyoto, the acting head of the African forces, said in a statement issued by the African Union.
Abdikadir Mohamed Sidii, the governor of the Lower Shabelle region in southern Somalia, where Barawe is located, had earlier told Reuters that Al Shabab fled when the forces marched on the town.
"We have settled most of the troops on the fringes of the town in order not to scare the residents. Only a few infantry are now inside. The mood is calm and there is neither attack nor resistance. Residents are calm," Sidii said.
Sheik Abdiasis Abu Musab, Al Shabab's military operations spokesman, declined to comment on whether the Islamist militants had abandoned the town.
He told Reuters earlier in the day that militants on Saturday had burned two government vehicles near Barawe. The AU said the ambush was not successful.
Hussein Nur, a university lecturer in governance and leadership in Mogadishu, said Barawe's loss was a blow to Al Shabab.
"Economically, it was a port where they exported charcoal and imported what they needed. Militarily, it was a strategic place where Al Shabaab leaders and foreigners hid and trained bombers," he told Reuters.
"For the government, it means Al Shabab no longer has a base in the range of about 200 km away from Mogadishu. However, this is not the elimination of All Shabab. They are still strong and control large swathes of Somalia."
Residents prepare to flee
Barawe, about 180 km (110 miles) south of Mogadishu, had been fully controlled by the Islamist militia with almost no government presence since 2006.
Al Shabab banned many aspects of modern life in the town and applied its strict literal interpretation of Islamic sharia law, ordering executions, floggings and amputations for crimes such as theft.
Residents said they were leaving Barawe.
"Al Shabab addressed us in the mosque ... they said they were leaving the town and warned us against helping the government," Hussein Ibrahim, a resident of Barawe told Reuters.
"I am also preparing to flee. We are sure Al Shabab will attack the town," he added.
The group ruled most of the southern region of Somalia from 2006 until 2011, when African troops marched into the capital. Western states, unnerved by the rising tide of Islamic militancy, have supported the AU peace-keeping force financially, saying Al Shabab exploited Somalia's chaos to train fighters.
Al Shabab was destabilized badly after it lost the southern port of Kismayo to AU and Somali government soldiers in September 2012.
Kenya, which has deployed troops with the African Union force, felt the impact of Al Shabab's reach in September last year when gunmen from the group launched an attack on the Westgate mall, leaving 67 dead.