Kenyan troops from the African Union force in Somalia entered the southern port of Kismayo for the first time Monday, witnesses said, three days after launching a beach assault that led Islamist insurgents to withdraw. Local clan militia had filled the streets since Saturday\'s rebel pullback, raising fears that the second city in southern and central Somalia -- which the Shebab had run for four years -- could descend into chaos. \"They arrived from the west of the city and are taking up positions,\" Aden Ismail, a local trader said. At least two other witnesses confirmed to AFP by phone that Kenyan soldiers from the 17,000-strong African Union Mission in Somalia (AMISOM) had entered the city, after remaining on the outskirts for more than two days. Kismayo was the main target of an operation launched by the Kenyan military almost a year ago. Its troops have since been integrated into AMISOM, whose bid to stamp out the insurgency is also supported by Ethiopia in western regions. Observers have said that reclaiming Kismayo would cut off the Shebab\'s supply lines, strip them of vital funding and spell the end of their ability to control large swathes of land in southern Somalia. The power vacuum created by what the Islamists called their \"tactical retreat\" -- after initially vowing the Indian Ocean would turn red with AMISOM blood -- had left Kismayo exposed to chaos and looming shortages. \"The town is very quiet this morning and there is no fighting ... but we have concerns about the clan militia roaming the streets,\" Ali Mumin, a resident, said before the Kenyan troops moved in. It was not immediately clear how many AMISOM troops were taking up position in Kismayo but residents had mixed feelings about the change. Asha Mohamed Aden, a seller of second-hand clothing, said she had seen \"heavily armed Kenyans\" entering the city along with Somali officers. \"They are carrying a lot of weapons,\" she said. \"Some people are happy to welcome them because they were fed up with the misrule\" of the Shebab Islamists,\" another resident Abdullahi Farey Hassan told AFP by telephone. \"But I will have my reservations until I see them doing something good. I hope they will be better than the Shebab,\" he said. 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. The group\'s pullouts from its other key bastions elsewhere in Somalia have heralded a return to guerrilla tactics, including suicide bomb attacks. Newly elected Somali president Hassan Sheikh Mohamud praised AMISOM Monday for forcing the Shebab to vacate the city. \"We commend AMISOM and the Somali troops who have shown bravery by forcing the enemy out of the town,\" a statement from Hassan\'s office said. Hassan also called on aid organisations to assist the thousands of Somalis displaced. Somali government sources said the administration is working on plans to mediate between the Somali clans who are arguing over the control of the town in order to facilitate an \"all inclusive administration\" and avoid further violence. \"Kismayo is a headache and the government is now planning to mediate between the clans to avoid civil unrest,\" a Somali government official told AFP on condition of anonymity. The Shebab used Kismayo as an export hub for the illegal charcoal trade and the port had been their de facto capital since they abandoned fixed positions in Mogadishu last year, also under increased military pressure from AMISOM. The port city has been largely off-limits for most foreign and local journalists and aid groups. Kismayo had also been a symbol of the extreme form of sharia -- or Islamic law -- the Shebab want to impose across the country since 2008, when they stoned a teenage girl in public on charges of adultery.