Yemen ship attack 'was terrorism'

However, the identity of the attackers of the Limburg oil tanker is still unknown, Yemeni sources close to the government investigation are reported to have said.

On Friday French investigators found traces of TNT explosives on the Limburg, providing the strongest evidence yet that the explosion on 6 October was due to a terrorist attack.

The tanker was carrying 400,000 barrels of crude oil when a blast ignited a fire on board, killing one crew member, and spilling 90,000 barrels of oil pouring into the Gulf of Aden.

Yemeni officials initially said the blast was an accident, not an attack.

Since the explosion, the French defence ministry has heightened security for French citizens in the Middle East, and has been considering military escorts for French commercial vessels in the region.

Terrorist hunt

On Friday, French Defence Minister Michele Alliot-Marie announced that "parts of a small boat and traces of TNT were found inside the tanker."

The findings backed up an earlier discovery of fragments from a small marine vessel on the deck of the Limburg.

Both discoveries are strong indications of a terrorist attack.

The Limburg is now thought to have been rammed by a small boat noticed by crew members shortly before the blast.

This style of attack resembles the suicide bombing of the US warship Cole in Yemen's Aden port in 2000, which killed 17 American sailors - an attack blamed on al-Qaeda militants.

So far, the investigators have not determined who was responsible for this week's attack.

The militant Yemeni Islamic group Aden-Abyan Islamic Army has claimed responsibility, but the US is sceptical of its claims.

American officials maintain the attackers are more likely to be linked to Osama Bin Laden's al-Qaeda organisation.

Al-Qaeda background

Yemen initially tried to dismiss reports the blast was deliberate.

But on Thursday the government conceded it could have been an act of terrorism.

"It might have been an arranged and deliberate act, and a meticulously planned one, for that matter," an unnamed Yemeni official told the Associated Press news agency.

In the past, Yemen has been a major recruiting ground for al-Qaeda.

But after the organisation was blamed for the attack on the USS Cole, the government has been co-operating with the Americans in cracking down on alleged terrorists.