Development Minister Francisco Alvarez Cascos took the initial decision to have the Prestige towed out to sea after it was holed in a storm off the northwestern Spanish coast last month, releasing a flood of foul-smelling fuel oil.

Officials said Cascos made the decision after consulting five civil servants, including a port captain and the head of the merchant navy.

As it was towed south, the tanker left behind a trail of thousands of tonnes of thick fuel oil that have coated Spanish beaches, devastating wildlife and shellfish and putting thousands of fishermen out of work. The tanker broke up and sank on November 19, creating another huge slick.

Some experts and environmentalists have said it would have been better to take the tanker into port where the oil on board could have been pumped out even though that would have undoubtedly polluted a section of coast.

A weary looking Aznar firmly defended Cascos's decision in a parliamentary session that was intended to focus on the Copenhagen European Union summit but turned into a raucous debate on the government's handling of the Prestige disaster.

Aznar came under strong attack from Jose Luis Rodriguez Zapatero, leader of the opposition Socialist Party, who said the government had been late to respond at all stages of the crisis.

Aznar highlighted the support pledged by Spain's EU partners to help it deal with the disaster, which involves as-yet uncalculated costs for cleanup and aid to out-of-work fishermen.

He estimated that EU aid from various programmes would total around 265 million euros ($270 million).

Fishermen along the Galician coast were mobilised again on Monday to face another slick threatening shellfish-rich bays.