French authorities have for the first time confiscated the passports of six nationals who were allegedly planning to travel to Syria to join jihadists.
Interior Minister Bernard Cazeneuve said the intelligence services believed the men wanted to join the Islamic State (IS) militant group.
The measure is part of new counter-terrorism laws adopted last November.
Meanwhile, France has deployed an aircraft carrier off Bahrain to be used against Islamic State (IS) militants.
Planes from the Charles de Gaulle carrier will be used against IS positions in Iraq, a spokesman for Defence Minister Jean-Yves Le Drian said.
The first Rafale fighter jet took off on Monday morning from the carrier as it sailed about 200km (120 miles) off the northern coast of Bahrain.
Correspondents say that the deployment of the warship will halve the time it takes for military aircraft - which normally fly from the United Arab Emirates - to reach Iraq.
France began Operation Chammal in support of the US-led coalition against IS in September.
Mr Cazeneuve said authorities had acted against the six men after their departure to Syria appeared to be imminent.
Their passports and identity cards have been confiscated for six months, after which the order can be renewed. They have the right to appeal against the move in court.
Analysis: Dina Newman, BBC News
France is not the only European country that can now confiscate passports from would-be jihadists to stop them from travelling to Syria.
In the UK, police can now seize the passports for up to 30 days from nationals trying to leave the country, and can temporarily prevent citizens suspected of involvement with Islamic State from re-entering Britain. The Home Secretary says she has removed passports from 25 suspected jihadists.
German law allows authorities to seize passports, but not personal identity cards that allow entry to EU countries and to Turkey - a gateway to Syria for jihadists. A new draft law would allow the removal of identity cards and their replacement with a document banning foreign travel.
In Sweden, the government is drafting a law that would allow the confiscation of passports from people known to have fought alongside jihadists in the Middle East.
According to French media, some of the men were reported to the authorities by relatives using a newly established telephone hotline, while others were identified by police investigations.
French officials quoted by the Reuters news agency estimate that about 400 French citizens are in Syria, 180 have returned to France, 200 want to go and 200 are somewhere in Europe trying to get there.
France has been on alert after 17 people were killed in attacks on the satirical Charlie Hebdo magazine and a Jewish supermarket in January.
UK officials think some 600 Britons have fought in Syria, with 300 having returned. Police can now seize passports for up to 30 days from nationals trying to leave the country, in addition to temporarily stopping citizens suspected of involvement with IS from entering Britain.
Last week, three British schoolgirls were said to have left London to travel to Syria through Turkey.
Turkish presidential spokesman Ibrahim Kalin said that Turkey was working intensively with the British authorities to trace the three schoolgirls.
Thousands of foreigners from more than 80 nations have joined Islamic State and other radical groups in Syria and Iraq, many crossing through Turkey. However, correspondents say they only represent a small amount of the total number of IS fighters.
Turkey has said it needs more information from the West if it is to intercept them. Mr Kalin said that his country had already deported 1,400 people suspected of attempting to join extremist groups.