France has seized the passports of six people for allegedly planning to leave the country to join armed groups in Syria, the first such bans since a sweeping anti-terrorism law was passed last year.
Interior Minister Bernard Cazeneuve said on Monday that about 40 others will also face travel bans in the coming weeks.
The six people prevented from departing the country have not been named.
"Today these six administrative bans on leaving the country have been signed, another 40 are in preparation," Cazeneuve told reporters outside the interior ministry.
"We wanted this measure ... because if French people leave to commit actions in Iraq and Syria, upon their return they represent an even greater danger for the national territory and risk committing wide-scale terrorist acts."
France has been on high alert since attacks on the offices of the satirical newspaper Charlie Hebdo and a kosher market in Paris last month, that killed 20 people, including three gunmen claiming ties to fighters in Syria and Yemen.
An interior ministry official said the passports and ID cards of the six have been declared invalid for six months, a measure that can be extended for up to two years.
The government estimates that about 1,400 French citizens have links to recruitment cells for Syria and Iraq, of which about 400 are already fighting with armed groups.
Some of the suspected fighters banned from leaving France on Monday were signalled to authorities through a hot line put in place last year, while others were identified through ongoing investigations, an aide to Cazeneuve told the Reuters news agency.
Suspects have the right to appeal the new measure in an administrative court.