But the ship's owners, Euronav SA, said they thought terrorists using a boat could have been responsible for Sunday's blast as the vessel prepared to take on a pilot and dock at Mina al-Dabah, near Mukalla in Yemen.

French investigators were due in Sanaa this week to take part in the probe. Yemen, which is trying to shed its image as a haven for militants from Osama bin Laden's al Qaeda network, took several days to declare the Cole bombing a terror attack.

"We are waiting for the investigation but, by elimination, it is very difficult to find a reason why it would have been an internal explosion," Captain Peter Raes, managing director of the management companies for Euronav's owners CMB told Reuters.

"The crew members are totally isolated. We tried to reach them but could not. They are under investigation," he said by telephone from Belgium.

All but one of the 25-member French and Bulgarian crew were rescued on Sunday and they are currently in Mukalla, some 800 km (500 miles) away from the capital Sanaa. The remaining crewman, a Bulgarian, has been declared officially missing, Raes said.

TOWERS OF BLACK SMOKE

Residents of Mukalla said thick towers of black smoke were still rising from the Limburg, which drifted overnight some 16 miles from shore. Raes said the ship, which has a gaping hole in its side, was not sinking as feared and was being towed to port.

Last month, the U.S. navy warned of possible attacks on oil tankers in Gulf waters by al Qaeda.

News of the blast stoked fears of instability in the Middle East and pushed world crude prices past $30 a barrel this week. Oil supplies were flowing uninterrupted from the vital region as shippers awaited word on the implications of the blast.

"As of now, it's business as usual," said a Gulf-based shipping executive. "Most of us feel this was a terrorist attack, but we still don't have the full story."

Limburg's charterer, Malaysia's state oil company Petronas, said the tanker was carrying 400,000 barrels of Saudi crude when it exploded and that it would have taken on another 1.5 million tonnes of crude at Mina al-Dabah. The company said it had covered its refining needs after the incident.

French President Jacques Chirac announced on Sunday that French investigators would join local experts in examining the tanker. A Yemeni official said the team was due this week.

Euronav, a subsidiary of Belgian shipping group Compagnie Maritime Belge (CMB), said the blast occurred while the Limburg was meeting a pilot vessel to bring it into the port.

"In my opinion, this was a terrorist attack," Euronav Director Jacques Moizan said on Sunday. "The crew saw a high-speed vessel approaching on the starboard side...an explosion followed with fire."

MEMORIES OF COLE ATTACK REVIVED

Yemeni Transport and Marine Affairs Minister Saeed Yafai said one of the ship's tanks exploded, igniting the fire. A Yemeni official quoted the tanker's captain as saying a small fire on board had set off the explosion.

Reports of a boat approaching the tanker revived memories of the Cole attack, which was rammed by suicide bombers in a boat packed with explosives. The attack killed 17 U.S. sailors.

Washington blames the Cole attack on al Qaeda and Saudi-born bin Laden, its chief suspect in the hijacked airliner attacks on the United States on September 11 last year.

Yemen has arrested more than 100 suspected members of al Qaeda and other Islamist groups since September 11.