An explosion that rocked a French oil tanker Sunday near Yemen in the Gulf of Aden is being investigated as a possible terrorist attack. News of the blast increased fears of instability in the Middle East and sent the price of crude past $30 a barrel Monday.

The Yemeni government ruled out an assault similar to the October 2000 suicide bombing of the USS Cole in Aden port, saying a fire aboard the French-flagged supertanker caused the explosion.

As the tanker was prepared to be tugged to port, the ship's owner, Euronav SA, said terrorists using a boat might have staged a bomb attack. The explosion cut a gaping hole in the ship's side.

Last month, the U.S. Navy warned shippers of possible attacks by Osama bin Laden's al Queda network on oil tankers in the Gulf and Red Sea, which see oil exports of about 15 million barrels per day - one third of international oil trade.

The tanker reportedly was carrying 400,000 barrels of Saudi crude when it exploded. It would have taken on another 1.5 million tons of crude at port.