A French oil tanker damaged by an explosion was towed into a northeastern Yemen port Friday, as investigators said metal and plastic pieces found on the deck suggested the ship was rammed by a smaller craft.

American officials said Sunday's blast was an act of terrorism most likely carried out by people with links to Al Qaeda, the terror network led by Usama bin Laden and blamed in the Sept. 11, 2001, attacks in the United States.

French Defense Minister Michele Alliot-Marie said in Paris that investigators found traces of TNT on the tanker Limburg.

The blast Sunday killed one crew member and spilled 90,000 barrels of oil into the Gulf Of Aden.

The tanker was brought into Mina al-Dabah port in Al Mukalla by three tug boats.

"It's become clear it's an act of terrorism," a U.S. intelligence official in Washington said Thursday on the condition of anonymity.

Al Qaeda would consider an oil tanker an economic target, the official said. Al Qaeda leaders have spoken of targeting the West's economy.

The attack bears a number of similarities to the suicide boat strike on the USS Cole in October 2000, the U.S. official said.

France's Foreign Ministry also said the ship had been attacked.

"The initial results of the inquiry carried out by French, Yemeni and American investigators suggest the explosion Oct. 6 on board the French oil tanker, the Limburg, was due to an attack," a statement said.

French investigator Jean-Francois Perrouty told French television channel France 3 on Thursday that debris found on the deck of the tanker did not come from the tanker.

"We found on the Limburg deck some parts mainly made of plastic and of a mixed glass-resin material used for constructing yachts and, in Yemen, fishing boats. We found that on the tanker deck along with some metal debris," he said.

Yemen's minister of sea transport, though, said the parts might have come from the tanker's own rescue boat.

"Investigators have indeed found fiberglass parts but they might be from the tanker's rescue boat that was damaged in the accident. The parts will be sent to laboratories to be tested and determine whether it belonged to the damaged boat," Minister of Sea Transport Saeed Yafaei said Thursday, according to the official Yemen news agency Saba.

Earlier, a U.S. defense official said several factors pointed to a terrorist attack: the hole in the ship is at sea level and the vessel is relatively new, making it unlikely that a malfunction caused the blast.

U.S. intelligence also picked up indications in recent weeks that terrorist groups remain interested in targeting maritime shipping, the defense official said.

Speculation that the incident was an act of terrorism arose shortly after the explosion, which spilled oil along 45 miles of coastline. The Limburg's captain later told The Associated Press a crew member saw a fishing boat approach the tanker shortly before the blast.

At first, Yemen, which has been eager to emphasize its commitment to the U.S.-led war on terrorism, sought to dismiss reports that the blast was deliberate.

But a Yemeni government official, speaking on condition of anonymity, said the investigation so far has yielded contradictory information and the blast may in fact have been an act of terrorism.

White House spokesman Ari Fleischer said Thursday, "We don't have any conclusions yet."

The pan-Arab daily Asharq al-Awsat reported Thursday it received a statement from a militant Muslim group claiming it attacked the ship. The paper said the Aden-Abyan Islamic Army claimed it carried out the explosion to avenge the execution of one of its leaders for the 1998 kidnapping of 16 Western tourists.

The Aden-Abyan Islamic Army was formed by Yemeni and other Arab fighters who, like bin Laden, helped Afghans oust Soviet invaders with U.S. help in the 1980s.

A Yemeni official, Abdul Kader Hilal, questioned the reported Aden-Abyan Islamic Army claim, saying the group does not have the means to carry out such an operation. But he said one of the group's members was among those detained for questioning.

U.S. counterterrorism officials also are skeptical of the Aden-Abyan Islamic Army's claim of responsibility, a U.S. intelligence official said in Washington, although U.S. officials believe the group has Al Qaeda ties.

Other, unspecified operatives with links to Al Qaeda are believed to have been responsible, the official said.