French police are holding 13 people following raids targeting militants suspected of having links to last year's suicide bomb attacks in Morocco.
The French special forces struck at dawn
Nine men and six women were initially arrested in two operations near Paris - but two of the detainees were subsequently released.
The arrests come as police investigate the deaths of three French nationals in the Casablanca attacks last May.
About 45 people - 12 of them suicide bombers - were killed in the attacks.
The dawn raids, mounted by the DST counter-espionage service, took place in the Paris suburbs of Aulnay-sous-Bois and Mantes-la-Jolie.
Some of the men detained are said to be linked to the Moroccan Islamic Combatant Group (MICG), French interior ministry sources said.
The MICG is believed to have carried out the Casablanca bombings.
Five simultaneous attacks killed 45 people in Casablanca
An offshoot of the group is also suspected of involvement in the Madrid blasts last month that killed 191 people.
However French prosecutors have said the
arrests were not linked to the Spanish investigation.
French terror suspects can be held for questioning for up to four days.
Hugh Schofield in Paris says it is not clear yet how much evidence the authorities hold against the 13 detainees.
It is common procedure for anti-terrorist investigators to carry out broad sweeps in the hope of turning up information - and many of those arrested are subsequently released without charge.
According to the US State Department, the MICG emerged in the late 1990s.
It says the group's aims include establishing an Islamic state in Morocco and that it supports al-Qaeda's "holy war" against the West.
The group is said to be based in Afghanistan, western Europe and possibly Morocco.