The end of NATO's mission in Libya has moved "much closer" following the killing of former Libyan leader Muammar Gaddafi and the fall of Sirte, the military alliance's chief said on Thursday.

"We will terminate our mission in coordination with the United Nations and the National Transitional Council (NTC). With the reported fall of Bani Walid and Sirte, that moment has now moved much closer," NATO Secretary General Anders Fogh Rasmussen said in a statement after Gaddafi's death.

Rasmussen said that the rule of Gaddafi has "finally come to an end" and Libya can "draw a line under a long dark chapter in its history and turn over a new page."

He called on Libyans to put aside their differences and work together to build a brighter future.

"I urge the National Transitional Council to prevent any reprisals against civilians and to show restraint in dealing with defeated pro-Gaddafi forces," he said.

A NATO official told Xinhua that NATO's decision-making body, the North Atlantic Council, will convene a special session on Friday to discuss its military operation in Libya.

It was in February that massive protests erupted in Libyan cities, including the capital Tripoli, demanding an end to the 42-year rule of Gaddafi.

NATO took the helm of the air mission against the regime in March after a UN Security Council resolution authorizing the enforcement of a no-fly zone over Libya.