Osama bin Laden has threatened France with terror attacks for passing a law that bans Muslim-style face veils.
A newly released audio tape of the al Qaida leader appears to be authentic, the French foreign ministry said.
The voice on the audio tape threatens to kill French citizens to avenge their country's support for the war in Afghanistan and in revenge for the veil ban. The tape was obtained by the Al-Jazeera television station.
The foreign ministry said the tape's "authenticity can be considered established based on initial verifications".
The message "only confirms that reality of the terror threat," a foreign ministry spokesman said.
A series of terror warnings has put France and other European countries on high alert in recent weeks.
Speculation on the source of a potential terror threat in France has focused on a group called al Qaida in the Islamic Maghreb.
That group, an offshoot of bin Laden's network, has claimed responsibility for the abduction of five French citizens in Niger and is believed to have taken them to neighbouring Mali. The French hostages, as well as a Togolese and a Madagascar national, were kidnapped on September 16 while they slept in their villas in the uranium mining town of Arlit.
About 4,000 French troops are deployed in and near Afghanistan.