BBC News' Kevin Connolly on the Europe-wide operation

Up to 50 people were arrested in France, mostly in the Paris area, but addresses in provincial cities including Lyons and Marseilles were also raided.

The searches were carried out on the orders of four French judges with responsibility for combating terrorism.

Similar operations took place in Germany, Italy, Switzerland and Belgium, where a further 40 people were arrested.

The French Interior Minister, Jean-Pierre Chevenement, said police broke up at least three networks providing logistical support for the Armed Islamic Group or GIA - the most violent of the groups seeking the overthrow of the Algerian government.

Middle East analyst George Joffee on the GIA in France

A separate interior ministry statement said the operation had been carried out after several months of surveillance that led police to "suspect the preparation of terrorist activity in the run-up to the World Cup."

French police sources, speaking on condition of anonymity, said the operation primarily had targeted networks loyal to Hassan Attab, a dissident GIA leader, who is suspected of trying to bring the Algerian conflict to Europe.

Among those arrested in France were two men considered to be Attab's top allies in Europe.

Propaganda value of attack

A BBC correspondent in Paris says that with two teams from North Africa playing in the World Cup finals starting next month, a successful attack by one of the militant Algerian Islamic groups would be an immense propaganda coup.

France suffered a series of bomb attacks in 1995, blamed on Islamic guerrillas, which killed eight people and injured more than 170.

In 1996, an explosive device killed four people in a Paris station of a commuter rail line.