U.S. Navy officers and French agents were being sent here to investigate whether a terrorist attack caused the explosion and fire that raged for hours aboard a French oil tanker, officials said Monday.

A State Department official, who spoke on condition of anonymity, said it looks as though the blast occurred inside the tanker. The damage suggested that "things were blown out" from the tanker instead of the other way around, the official said.

Others had suggested that a small boat laden with explosives may have struck the tanker and caused the blast in an attack similar to that on the USS Cole two years ago in the Yemeni port of Aden. The attack on the Cole killed 17 U.S. sailors and was blamed on Usama bin Laden's Al Qaeda terrorist network.

The United States was not ruling out terrorism as a cause of Sunday's blast. But if initial suspicions of an internal explosion are borne out, that would "lead to the conclusion that it probably was an accident," a senior official in Washington said.

The Yemeni government said the blaze was an accident caused by an oil leak, but the ship's owner disagreed, saying it was a "deliberate act." French officials said it was still too early to rule out terrorism.

"The fire has been extinguished. We believe the explosion happened from within the tanker, but investigations are still under way," a Yemeni official said Monday on condition of anonymity.

Strong winds during the night had pushed the tanker, the Limburg, further into the sea and away from its destination, Mina al-Dabah, a port close to the city of Al Mukalla, about 200 miles southeast of the capital, San`a. One of the ship's sides was badly burned and had a hole about three feet across.

Officials accompanying journalists on a small boat taken close to the Limburg said it was the only hole. The twisted metal around the hole pointed outward, perhaps an indication the explosion was inside the tanker.

The intense heat of smoldering crude forced technicians trying to assess the damage to keep their distance from the tanker. Nearby, two tugboats awaited orders to take the tanker to port.

Yemeni Prime Minister Abdul-Kader Bajammal formed a special committee to investigate the blast. The Yemeni official said Yemeni and French investigators would cooperate in the probe.

In Paris, the anti-terrorism section of the prosecutor's office opened a preliminary investigation Sunday, judicial sources said, adding that agents from France's counterterrorism service were to head to Yemen to investigate.

The State Department official said U.S. Navy officers were also being sent to the scene to help out with the investigation. It wasn't immediately clear whether Navy investigators invited themselves or were asked to join in the investigation.

The French newspaper Le Monde quoted a source close to the investigation as saying that a "very long, strong blast" tore a hole in the ship's hull 10 yards across.

Operations at the port were normal Monday, with no security forces or coast guard in sight and commercial fishing boats heading out to sea.

France's foreign minister said Monday that the possibility that the fire was deliberately set has not been ruled out.

"Nothing has been excluded," Dominique de Villepin told RTL radio.

A day earlier, the French foreign ministry said it did not have "enough elements to allow us to formulate a ... hypothesis which would point to a terrorist attack."

"It's a serious issue, a serious matter, and we have to wait for the first concrete results of the police research," said ministry spokesman Francois Rivasseau.

According to Yemeni officials, the captain of the Limburg said the fire started on his tanker and was followed by an explosion while crewmen tried to get the blaze under control.

In France, officials with Euronav, the company that owns the Limburg, said their understanding was that the captain saw a small fishing boat pulling up to the tanker before the blast at 9:15 a.m. local time. The officials speculated the fishing boat could not have caused such a huge blast unless it was carrying explosives.

There were also reports the explosion occurred as a pilot boat was preparing to escort the tanker into Mina al-Dabah.

"We believe it was a deliberate act. It was not an accident," Euronav director Jacques Moizan told The Associated Press.

Crude oil futures rose 24 cents higher on news of the explosion and fire to $29.86 per barrel early Monday on the New York Mercantile Exchange. Traders said they were awaiting more details.

"We'd feel a whole lot better if the government just came out and said it was not a terrorist attack," said John Kilduff, an oil analyst at Fimat USA.

Mina al-Dabah, about 200 miles east of Aden, is relatively quiet and is mainly used by tankers to load oil.

Yemen has been eager to emphasize its commitment to the U.S.-led war on terror and shake off its reputation as a hotbed of extremism -- it is believed to have been a longtime base for suspected Al Qaeda members and is the bin Laden family's ancestral home.

Security has been tightened at Yemeni ports since the attack on the Cole.

The Bahrain-based Maritime Liaison Office, which coordinates communication between the U.S. Navy and the commercial shipping community in the Gulf and Arabian Sea, issued an advisory in September warning ships of the possibility Al Qaeda was planning attacks on oil tankers.

The U.S. Navy's 5th Fleet has aircraft carriers, destroyers and other ships in the Gulf and Arabian Sea. A Bahrain-based spokesman for the fleet said Sunday the tanker fire had prompted no changes in U.S. security measures.

Euronav said the Limburg's crew of 25 included eight French and 17 Bulgarians. One Bulgarian was missing and the rest of the crew were in a hotel in Yemen, said Alain Ferre, Euronav's financial and administrative director.

Ferre said some crew members jumped into the water and were rescued while others first tried to put out the fire.

The Yemeni government asked the Canadian oil firm Nexen Inc. to help clean up an oil spill that resulted from the fire and explosion.

The Malaysian firm Petronas said in a statement Monday that it had chartered the Limburg. Petronas said it loaded about 400,000 barrels of crude in Saudi Arabia and was planning to load 1.5 million more barrels in Yemen, cargo purchased for the Malaysian Refining Co. in Melaka, Malaysia.

In Malaysia on Monday, a police official said on condition of anonymity that officials there did not believe the Limburg fire was a terrorist attack on Malaysia -- a largely Muslim country that has cracked down on Islamic militants and terror suspects.