France's interior minister says police have detained four people in a counterterrorist operation targeting those suspected of trying to join Islamist extremists abroad.

Manuel Valls said on France's BFM television Tuesday that an operation is under way in the Paris region, linked to the arrest of a French citizen in recent months on the Mali-Niger border. No details were immediately available.

Valls said French authorities are worried about French extremists joining rebels in Syria or the desert region around northern Mali, where Islamist radicals seized power last year and imposed harsh rule on local populations.

France, which fears northern Mali could become haven for international terrorists, launched a military intervention there last month after the extremists starting advancing toward the capital.