Robert Fisk: Israel's promise of humanitarian corridors is exposed as a sham

So much for Ehud Olmert's "humanitarian corridors". Two weeks after the Israeli Prime Minister's comforting assertion - which no one in Lebanon believed - the Israeli air force has blown up the last bridge across the Litani river, in effect ending all humanitarian convoys between Beirut and southern Lebanon. Requests from humanitarian organisations for clearance from the Israelis are now being refused. Even the Red Cross admits there is now, in effect, a blockade on a vast area along the Lebanese border where thousands of civilians are still cowering in their homes.

David Shearer, the UN's humanitarian co-ordinator in Lebanon, has pleaded with the Israelis to end their attacks against the country's infrastructure and end all activities which threaten the transport of humanitarian aid to the displaced. But convoys since have been cancelled or forced to make long detours across the country and along the edge of the Lebanese-Syrian border. Truck drivers are frightened to risk their lives under Israeli air attack. I myself was on a Red Cross field trip from Qlaya to Jezzine when, close to the village of Arab Selim, an Israeli jet dropped a bomb on the road 80 metres in front of us. On the Litani river, north of Tyre, the main road bridge had been blasted away but the Lebanese army had constructed a temporary bridge over the water to the west. Now that, too, has been ripped to pieces by Israeli bombs.

Mr Shearer warned of a "serious humanitarian crisis" if convoys were not allowed to move south. A Red Cross spokesman, Richard Huguenin, said his organisation had been denied permission by the Israelis to move humanitarian aid to the border. Without guarantees of safe passage, the organisation cannot leave Tyre for dozens of villages whose inhabitants are trapped. "At night, we ask for permission and in the morning we get either a red light or a green light, and for the past 48 hours it has been red," he said.

A Greek ship carrying Red Cross supplies was supposed to have docked in Tyre on Monday, but was refused permission to land and diverted to Sidon, north of the Litani. The French are still bringing boatloads of supplies into Beirut, accompanied - wisely, it has to be said - by a French warship equipped with anti-aircraft missiles.

So are Mr Olmert's non-existent "humanitarian corridors" to be created by force? Or will they have to wait until the civilians of southern Lebanon are starving?