Fighting resumed yesterday in the Gaddafi stronghold of Sirte after a two-day lull during which hundreds of civilians streamed out of the besieged city. Refugees and aid workers gave harrowing accounts of death and deprivation, with street-to-street combat, and food, water and medicine running desperately low.

Anti-Gaddafi fighters claimed that the new offensive is the final assault; and there can be little doubt that, once Sirte falls, the war for Libya is won. The rest of the country is in the hands of forces who owe allegiance to the National Transitional Council. Sirte and small pockets around it are all that remains of the Gaddafi clan's erstwhile power.

Yet Colonel Gaddafi and his stalwarts have proved far harder to dislodge than anyone probably envisaged – including the leaders of the government that is still waiting to replace them. It is six weeks now since Tripoli fell to what were then described as the rebel forces, amid rejoicing and localised battles that were mercifully brief. But the euphoria that prevailed then has long faded, and with it the sense of urgency about forming a new government and building the new post-Gaddafi Libya. The transfer of the whole government from Benghazi to Tripoli has been postponed several times, and now even the announcement of its composition is on hold until the Gaddafi forces have been defeated.

This loss of momentum is regrettable, but the delay in formally constituting the new administration is as wise as it is realistic. To declare victory while a part of the country is still in Gaddafi's hands is to risk charges of hubris and invite unpleasant surprises later.

When Gaddafi insisted that he would fight to the end, he appears to have meant exactly that. The long siege and street-fighting that were grimly predicted for Tripoli have been visited instead on Sirte. And as the fighting goes on, the risk of mass killings and revenge attacks on both sides rises. It is crucial for the post-war credibility of the anti-Gaddafi forces that they resist these temptations. Nor should they rely on increased outside intervention. Nato's mandate remains what it was: the protection of civilians. The last battle to secure the new Libya must be one that the new government is seen to win for itself.