The first Somali government and African Union troops are reported to have entered the strategic Somali port of Kismayo, witnesses have told the BBC.They have been battling the al-Shabab militia for control of the city.On Saturday, the al-Qaeda aligned militants said they had withdrawn from Kismayo after an AU military assault. Kenyan and Somali forces had launched an attack on the Islamist group’s last major bastion the day before, encountering fierce resistance.Reports as to the size and make up of the AU contingent have been mixed.One resident told the BBC Somali Service that a small infantry unit of 11 Somali soldiers had entered the city from the west and were patrolling on foot on the main roads of Kismayo, while another said he had seen both Kenyan and Somali troops entering the city centre from the airport.A spokesperson for the Somali government forces, Mohamud Farah, told the Reuters news agency that they had sent "450 [troops] to patrol the town and settle the police headquarters”.Kenyan troops are part of a force trying to wrest control of Somalia from militants for the new United Nations-backed president.After resisting the AU and Somali advance on Friday, al-Shabab announced it had shut its five-year administration in Kismayo the next day for strategic reasons.