The French authorities have encountered further difficulties in trying to contain possible environmental damage from a tanker which broke up in the Bay of Biscay.

The stern section of the Erika has sunk while being towed towards deeper waters.

The forward section slipped beneath the waves earlier but is believed to be drifting and French officials have called for international help to recover it.

They are still trying to determine if the wreck has gone deep enough for any oil still leaking to be absorbed by the sea.

The officials said there was no immediate danger of pollution to the Brittany coast. A slick of 4,000-5,000 tonnes of oil that escaped from the tanker was being carried out to sea by currents and winds.

But pollution experts had conflicting views, one saying the waves could "pulverise" the oil and another saying the thickness of the oil was a worry.

An aircraft of the customs service is keeping watch on the slick which is reported to be drifting southwest into the Bay of Biscay.

Helicopter rescue

The Maltese-registered Erika, which had been carrying more than 20,000 tonnes of diesel oil, split in two 45 miles (70km) south of Brittany's rugged Finistere Peninsula on Sunday morning in 100km (60-mile) winds and 6m (20ft) waves.

Twenty-six Indian crew members were winched to safety by helicopter, after a distress call was received by the French coastguard at about 0500 GMT on Sunday.

British Royal Navy Sea King helicopters were called to the scene, because the French feared they did not have enough aircraft to carry out the rescue.

"It was very rough. The bow of the tanker was in one place and the superstructure was about a quarter of a mile away," said Lieutenant Fraser Hunt, one of the British helicopter pilots.

It was not clear why the Erika broke up, but the ship was reported to have already been forced to put into port at Donges in southwest France after it had problems with listing.

The captain cited "very serious structural problems" when he radioed for help, the port authorities in Brest said.

The 180m (590ft) ship, owned by Italy's Panship Management, was bound for Italy from the northern French port of Dunkirk.

In 1978, Brittany witnessed the worst oil disaster in history when the Amoco Cadiz spilled an estimated 246m litres (65m gallons) off the coast.