The salvage of the Russian nuclear submarine Kursk from the bottom of the sea has run into further delays. For the third time, divers were forced to repair an underwater saw needed to cut off the bow of the sub.

The bow of the Kursk is being sliced off and until this operation is completed, the rest of the 18,000 ton vessel cannot be raised.

However, equipment failure has halted work three times, as the state of the art diamond saw required repairs. Twenty-four hours were lost during the last episode, when the saw became jammed, and divers had to winch it free as they worked in Arctic waters, 100 meters beneath the Barents Sea.

The Russian navy predicts the operation to slice the submarine in two will be completed this weekend. But the international team of divers is racing against time to meet the mid-September deadline for lifting the vessel.

The international consortium working on the salvage concedes that work is behind schedule. But the Russian government insists that the operation will be completed this year, in October if necessary.

But by then the Arctic winter will make conditions extremely difficult, and perhaps impossible. Bad weather has already caused delays even during the summer months.

Raising such a huge vessel, with a dangerous cargo of missiles and two nuclear reactors, has never been attempted before.

The Kursk sank one year ago during training exercises, with the loss of all 118 men aboard. Russia says it still does not know what caused its worst peacetime naval catastrophe. It considers a collision with a foreign vessel as a likely cause.

However most independent experts believe an explosion in the torpedo bay probably caused the submarine to sink.