AL-MUKALLA, Yemen - The explosion which crippled a French supertanker off Yemen was not an accident, the ship's captain insisted today as French experts were set to join investigations into the exact causes.

"The way the explosion happened it could not be due to a technical problem," Hubert Ardillon told reporters.

"A member of the crew told me he saw a small boat approach and I believe him," the Limburg's master said.

"At least the first explosion occurred on the outside of the ship. I am positive about that. I saw it.

"I totally rule out the theory of an accident."

The French embassy in Sanaa said the damage was caused by a small boat packed with explosives that rammed the tanker on Sunday, recalling the Oct 12 Islamist attack two years ago on the US destroyer Cole in Aden harbour which killed 17 men.