The allied air assault on Muammer Gaddafi’s forces followed with impressive speed after the UN Security Council authorised the action last week. The attacks are justified. Responding instantly to the resolution, the Libyan regime announced a ceasefire and said it would comply with UN demands. It plainly had no intention of doing so. It pressed on with its attacks against rebel-held areas. The international coalition turned to force, and was right to.

Bringing this just and measured intervention to a successful end may make severe demands. One can hope that Col Gaddafi folds quickly, but he may not. He has promised a long war. For the moment, allied air strikes have stalled his assault on Benghazi, but the Libyan leader has given no sign of ending his war on fellow Libyans. How much real support he commands in the country is hard to say, given the ferocity of his repression in the areas he controls. The allies should be prepared for a prolonged involvement.

They must also stay united, which makes it disturbing that cracks in the coalition have already appeared. On Sunday, Amr Moussa, the head of the Arab League, told reporters that coalition air strikes had gone further than the league had intended when it lent its support. The idea, he said, was to protect civilians with a no-fly zone. The force deployed was excessive.