PARIS, May 2 (AFP) - France on Monday set up a crisis cell on the eve of a deadline set by the shadowy AZF group, which in March threatened train bombings - a new "Madrid tragedy" - if Paris did not fulfil its demands for money.  

"Save yourselves from the Madrid tragedy," said the group, in reference to the March 11, 2004, train bomb attacks in Spain that killed 191 people.  

"Do not compromise your fellow citizens' security," it said in a letter sent on March 15 to both French President Jacques Chirac and the interior ministry.  

"From May 3, we will again be in contact with you," the group - or individual - wrote, adding that it expected a response to its eventual demands "within a short period of time".  

The letter did not specify a monetary amount demanded by the group.  

Interior Minister Dominique de Villepin, whose ministry has set up the crisis response team to coordinate dealings with AZF, said: "Our services are mobilized to act discreetly."  

The March letters bore a different logo but used the same code name as a group that first appeared in December 2003, threatening to blow up French railway lines unless it was paid millions of euros in cash.  

The February 2004 discovery of a sophisticated bomb hidden under stones on a train line between Paris and Toulouse underlined the seriousness of the initial AZF threat.  

Police and the first group of blackmailers communicated via classified ads in the daily press, lending a veneer of intrigue to the case, which was only heightened with the failure of a complex ransom drop in March 2004.  

On March 25 last year - one day after another of its devices was found on a railway line - AZF suspended its actions, but warned it would be back with a more effective "force of persuasion".  

The name AZF is believed to refer to the AZF factory in the south-western city of Toulouse that was destroyed in an explosion in September 2001. The blast killed 30 people and injured more than 1,000.