France has barred six people from leaving the country because they wanted to join extremists in Syria, the first such travel ban under a new law aimed at keeping French radicals from gaining violent experience abroad.

Interior Minister Bernard Cazeneuve says some 40 others will face travel bans in the coming weeks. He did not name the six.

The bans issued Monday are the first since a sweeping anti-terrorism law passed last year. The government is especially worried since attacks in Paris last month killed 20 people, including three gunmen claiming ties to Islamic extremists in Syria and Yemen.

An Interior Ministry official says 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.