The Islamist fighters said Saturday they had made a "tactical retreat" from Kismayo. But the Kenyan and Somali soldiers whose advance towards the city forced the Shebab's withdrawal have not yet arrived, leaving the city exposed to chaos.

Since the departure of the Islamists, who ruled the city with an iron fist, unidentified gunmen have killed at least three civilians, including a traditional leader, according to residents interviewed by phone from Mogadishu.

"Three civilians were killed, including a traditional elder, by unidentified gunmen, and the town has been very tense since yesterday," said one resident Abdulahi Adan, adding Kismayo was rocked by heavy explosions overnight.

Another resident, Mohamed Issaq, said on Saturday that at least four civilians had been killed, including two clan leaders.

"There is power vacuum and armed clan militia have started regrouping," said Dahir Moalim, another resident. "There were gunshots last night and most of the people did not sleep because of the tensions."

Residents said there was still no sign of African Union troops in the southern city.

"People are in the streets eagerly waiting to witness the changes but so far the Kenyan troops and the Somali soldiers are in the suburbs of the town," said Shueyb Mohamed.

The Somali military's second in command, General Abdikarin Youssouf Dhegobadan, said the troops are working on removing security threats before moving into the city.

"Our forces will peacefully walk into the city very soon, but before that there are new plans underlined to tackle the booby traps that are likely planted by the Al-Qaeda militants," he said.

"The city is already secure but to safeguard the protection of the civilians there should be a sober way of entering the town."

The fall of Kismayo is the latest in a string of major losses of territory over the past year for the Shebab, which have switched to guerrilla tactics as they lost their strongholds.

The Islamists have been battling Somalia's fragile Western-backed government since 2007.