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.