Kenyan helicopter gunships struck Shebab bases outside the Somali port of Kismayo to clear the way for a takeover of the town abandoned by the Al-Qaeda linked Islamist fighters, the army said Sunday. Residents said Kismayo was in the grip of lawlessness and a power vacuum, with gunmen killing at least three people since the Shebab pulled out of the city on Saturday, their last bastion to fall. The Kenyan army said helicopter gunships were attacking Shebab bases outside the city ahead of a final ground assault to occupy the strategic southern city after an advance by Kenyan and Somali troops forced the Islamists out. However, the power vacuum created by what the Islamists called their \"tactical retreat\" left Kismayo exposed to chaos as residents waited for the Kenyan and Somali forces to arrive. Since the retreat of the Shebab, who ruled Kismayo 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 that Kismayo had been rocked by heavy explosions overnight. Another resident, Mohamed Issaq, said 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, where the Shebab reportedly busted open the gates of the main prison and the police station before retreating. \"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 Kenyan army said it was doing everything possible to ensure its forces took control of the city \"safely\" and \"in good time\". \"We have received reports of the lawlessness within parts of the city... We want to assure the civilians of Kismayo that their calls for order have been heard,\" Kenya Defence Forces spokesman Cyrus Oguna told AFP. Oguna said that late Saturday other Shebab bases outside Kismayo were destroyed by helicopter gunships and that the Shebab suffered \"heavy casualties\". \"In Bardhere, there was a congregation of new Shebab recruits.... We struck them as they were receiving final instruction from their commanders,\" he said. Oguna said there were other air strikes in Berhane, a town near Kismayo, \"to clear the path for a ground assault.\" The fall of Kismayo is the latest in a string of major losses of territory over the past year for the Shebab, who have since switched to guerrilla tactics after they lost their strongholds. Kismayo had been a key source of revenue in the form of charcoal exports, as well as the main entry point for weapons for the Islamists who have been battling Somalia\'s fragile Western-backed government since 2007. The Somali military\'s second in command, General Abdikarin Youssouf Dhegobadan, said troops were 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.\"