Rivals of French Prime Minister Jean-Pierre Raffarin accused him on Thursday of exaggerating the terror threat facing France in a bid to win support ahead of key regional polls this weekend.

Opposition Socialists said he sought to exploit a climate of fear after the Madrid train bombings by publishing a threat to France made by a shadowy Islamic group whose authenticity has since been questioned. Raffarin allies issued vehement denials.

Manipulating the issue could backfire as it did in Spain, they warned. Although Raffarin's government is not at stake in the polls, a voter backlash could force a cabinet reshuffle.

"There are enough issues in these elections...without playing the game of terrorist threats, namely of using them for electoral ends," Socialist Party chief Francois Hollande told France Inter radio.

"The French right should look at what happened in Spain and not copy something that would be viewed very poorly in France," he said of anger over the Spanish government's handling of a suspected al Qaeda-linked attack in Madrid that killed 201 people.