Interior Minister Nicolas Sarkozy said the letter threatening to plunge France into "terror and remorse," addressed to Prime Minister Jean-Pierre Raffarin, was being taken seriously. A group calling itself, 'Servants of Allah, the Powerful and Wise One' sent the message via two French newspapers. Mr Sarkozy said that according to the French intelligence services, the letter "does not bear the hallmarks of phrasing customary to Islamic extremists." However,"we take every threat seriously," he added.

    The letter was sent to two leading French newspapers - Le Parisien and Le Monde. The editor of Le Parisien, Jacques Esperandieu, told the BBC's World Today programme that it had been posted in central Paris on Monday and "there was nothing strange about the envelope." It did not mention last week's train bombs that killed 201 people in Madrid, he said. But it mentioned February 10, 2004 several times - the date France passed the new law, banning Islamic headscarves from schools. Since that date France had "joined the list of most ardent enemies of Islam," it warned. It called the "veil ban" a "declaration of war to the Muslim world" and called on Mr Raffarin to withdraw it.

    Both Le Parisien and Le Monde said the letter was signed "Mosvar Barayev commando." Movsar Barayev was the leader of a Chechen group that took hundreds hostage in a Moscow theatre in October 2002, and died during the siege.

    The letter "made sense, sounded coherent and was structured in such a way that I thought it could be serious," Mr Esperandieu said. It warned that "a heavy offensive will take place on the grounds of the allies of Satan and we are going to plunge France into terror and remorse."