On Sunday, ICC Chief Prosecutor Luis Moreno-Ocampo said President Bush and UK Prime Minister Tony Blair may one day face war crimes charges before the International Criminal Court (ICC) at The Hague. Moreno-Ocampo said that the ICC could investigate allegations of war crimes stemming from the conduct of coalition forces in Iraq, so long as Iraq agrees to ratify the Rome Statute and accede to ICC jurisdiction.

In an opinion piece in the newspaper El Pais, published on the fourth anniversary of the U.S.-led invasion, Spanish judge Baltasar Garzon said the war was "one of the most sordid and unjustifiable episodes in recent human history".

"We should look more deeply into the possible criminal responsibility of the people who are, or were, responsible for this war and see whether there is sufficient evidence to make them answer for it," Garzon wrote.

"There is enough of an argument in 650,000 deaths for this investigation and inquiry to start without more delay," he said.

Garzon, who became famous in 1999 when he tried to extradite Pinochet from Britain and try him for crimes against humanity, was particularly critical of the former Spanish government, a major backer of the Iraq invasion.

In February, Spain's former leader Jose Maria Aznar said he now knew Saddam Hussein had no weapons of mass destruction but "the problem was not having been clever enough to know earlier."

Garzon wrote: "If he didn't know enough, he should be asked why he didn't act prudently, giving United Nations inspectors more leeway instead of doing the opposite in total submission and fidelity to President Bush."

Gaspar Llamazares, head of the left-wing party Izquierda Unida, said he would present a motion to the Spanish parliament that leaders behind the war should face international tribunals.

"People cannot be allowed to make decisions that cause hundreds of thousands of victims, fail to recognise their errors and not have to answer to a court," said Llamazares, whose party is allied to the ruling Socialist party.

Garzon, who took a sabbatical last year to study international terrorism, said the Iraq war had helped incite hatred and garner more support for terrorist training camps.

"In some way, with a terrible lack of awareness, we have been and are helping this monster grow more and more and strengthen by the minute so it is probably invincible," he said.