A previously unknown terror group is threatening to blow up French railway tracks unless it is paid millions of dollars, authorities said Wednesday.

Information from the group led to the recovery on Feb. 21 of an explosive device buried in the bed of a railway line near Limoges (search) in central France, the government said. The bomb would have been powerful enough to break a track, it said.

The government had earlier urged French and international media not to report the blackmail effort to protect efforts to establish contacts with the group. But the Interior Ministry released details about the threats in a statement Wednesday after the story leaked.

The group "has sent several letters demanding an important sum of money in exchange for neutralizing several bombs it says it has laid, notably under rail lines," the ministry's statement said.

Police said the group threatened attacks unless it receives $4 million and €1 million — worth $1.2 million — within days. Police do not believe the group has any connection to Islamic terror networks.

Anti-terror magistrates are investigating.

The Interior Ministry said the group identifies itself as AZF (search) — the same initials as a chemical factory that exploded, killing 30 people, in southwestern France in 2001. Investigators believe that explosion was accidental.

AZF "presents itself as a 'pressure group with terrorist characteristics,'" the ministry's statement said.

Police are working the case, but "hope to do it with discretion to give themselves the maximum of chances" for success, the ministry said, without elaborating on the investigation.