AL MUKALLA, Yemen -- The captain of a French oil tanker that exploded and caught fire off Yemen said Tuesday that a crew member saw a fishing boat approach the vessel before the blast, leading him to believe it was attacked. But Yemeni officials say there is no evidence of an attack.

Hubert Ardillon has maintained he believed the explosion Sunday was a deliberate act, while U.S. and Yemeni officials have said it was probably an accident, though they have not ruled out anything.

"My position could not allow me to see any boat approaching the tanker Limburg's side, but one of my crew members saw it," Ardillon told The Associated Press.

"I heard an explosion, then a fire started, and then I heard three or four explosions, each 45 minutes apart," he said.

The chief Yemeni investigator, Minister of Sea Transport Said Yafaai, called the captain's statements "irresponsible," and said nothing learned so far suggests terrorism.

"Our visit to the ship today did not change our previous position," Yafaai told reporters. "We should wait for the results of the investigation."

Shortly after the explosion, Yemeni officials had quoted Ardillon as saying a fire broke out on board the Limburg first, setting off the blast.

But speaking from a hotel in Al Mukalla, the captain told the AP on Tuesday that the fire followed the explosion. He refused to comment on the earlier reports he had said otherwise.

Yemeni and French counterterrorism investigators sent from Paris will begin the "practical steps" for a joint investigation on Wednesday, Yafaai said, adding that Yemeni investigators will share with them all information they have gathered.

A team of U.S. investigators also arrived in the Yemeni capital, San'a, on Tuesday and headed to Al Mukalla to take part in the probe. Yafaai said they would "work as advisers to us in the investigation."

"Nothing so far suggests it was a terrorist act," said Yafaai. "If it was a deliberate blast, the combination of explosive material and oil would have resulted in a much bigger blaze."