Updated

Authorities say four French citizens, including two men who spent time in Syria, have been arrested in southern France as part of a terrorism investigation.

The Interior Ministry says two women were among those arrested Tuesday morning in the Gard and Vaucluse regions. It said the four were wanted for questioning by an anti-terrorism judge for alleged criminal association in view of preparing a terror act, without specifying.

The arrests bring to 15 the number of people detained in Europe in less than a week on terror-related suspicions, including eight in Spain, three in Germany, and a wounded Frenchman returning from fighting in Syria.

European authorities are concerned that their citizens who fought with jihadi groups in Syria's civil war could return home with intentions to carry out terror attacks.