TRIPOLI (AFP) - A special envoy for UN Secretary General Ban Ki-moon arrived in Tripoli on Saturday, as the international body and Libya's new leaders stepped up efforts to bring order and democracy to the country. Ian Martin landed at a military airbase in the capital, after Ban said the world body was ready to assist in re-establishing security following the nearly seven-month uprising that ousted Moamer Gaddafi. "I am here now to discuss with the National Transitional Council how the United Nations can be most helpful in the future," Martin told reporters on arrival. "I think the future leaders of Libya face a very big challenge, they have already shown the ways in which they are ready to tackle that challenge and it will be the commitment of the United Nations to assist them in any way they ask." Almost two weeks since anti-Gaddafi forces overran Tripoli, there were signs of life returning to normal in the capital. "We are ready to serve our country again," said 22-year-old officer Abdulkader Ammar, on patrol for the first time since Gaddafi's fall. "The war is over and we have to go back to work," Abdullah Turki, a member of the NTC's stabilisation team told AFP. "It will take time, but it will come, people are eager to participate in rebuilding Libya." There was still no firm word on the whereabouts of the toppled strongman after he defiantly threatened to lead a protracted insurgency in audio tapes aired by Arab media on Thursday. The victors extended until next weekend an ultimatum for the surrender of remaining loyalists to give time for negotiations to bear fruit, but moved troops towards Bani Walid, southeast of the capital, where they suspect Gaddafi may have taken refuge. Some 600 men aboard 200 combat vehicles moved to within 20 kilometres of Bani Walid without meeting any opposition, before returning to their base in Misrata, fighters said. Abdulrazzak Naduri, deputy chief of the military council in Tarhuna, between Tripoli and Bani Walid, said tribal chiefs had been given until 0800 GMT Sunday to surrender the town.