African Union and Somali government troops stepped up their assault on al Shabaab fighters in the capital\'s northern outskirts on Wednesday, forcing hundreds of families to flee their makeshift homes and head for the city centre. The AU force, which already controls most of the capital, is trying to advance through the Afgoye corridor, once a rural area northwest of Mogadishu but now home to hundreds of thousands of Somalis uprooted from their homes. The corridor, believed to house the largest concentration of internally displaced people in the world, stretches some 30 km northwest of Mogadishu to the al Shabaab stronghold of Afgoye. The AU force began its advance on Tuesday and seized part of Tre Disho village, 13 km from the capital. Burundian troops with the African Union Mission in Somalia (AMISOM) were advancing from Tre Disho towards Elasha and Afgoye on Wednesday but were meeting resistance from al Shabaab fighters, their spokesman Captain Ndayiragije Come said. \"We want to capture Elasha and if not delayed by resistance we shall capture Afgoye. We captured two anti-aircraft guns hooked on cars and destroyed one yesterday. We also see about 40 bloated dead bodies of al Shabaab lying under the shrubs. They were killed in yesterday\'s battle,\" he said. Al Shabaab has waged a five-year campaign to topple Somalia\'s Western-backed government. It still controls swathes of central and southern Somalia but is being gradually squeezed out of its strongholds by Kenyan and Ethiopian troops who have launched their own incursions into Somalia, and is being pushed out of Mogadishu by AU forces. Civilians fleeing the fighting hoped to find safety in central Mogadishu. \"We fled with the children early in the morning,\" Farhia Aden, a mother of two, told Reuters in Bakara market. \"We couldn\'t stay there because shells were landing and bullets were buzzing around us.\" \"People are panicked ... we had no time to take all our things,\" she added. Road blocked Another resident, Hussein Farah, said he had seen many rebels aboard vehicles, some with machineguns on their shoulders. \"It may take time for the government to control that area,\" he said at the Ex-Control checkpoint where Somali soldiers stopped his family from entering the capital. Somali police officer Capt. Ahmed Nour said government forces had blocked the road because they did not want civilians to get caught in the shooting. \"There is military movement along the road. Many families have already come in and we shall give access to the remaining ones later when we reopen the checkpoint,\" he said. The African Union has said that by securing the Afgoye corridor it would give some 400,000 people access to aid. Al Shabaab could not be reached for comment on Wednesday, but on Tuesday the group said its fighters had killed about 30 soldiers. It is difficult to verify either side\'s estimates of casualties, which are often exaggerated. A Reuters witness, at an airstrip in Mogadishu where the offensive was launched, said he had seen two dead Somali soldiers and two wounded Burundian ones on Tuesday.