Police and anti-terrorism investigators have been alerted to the possibility that small groups of ISIS extremists have left Syria for France and Belgium with plans to stage attacks.
Belgian intelligence services sent a note to French counterparts about the possible groups, and it was sent to police and anti-terrorism forces across France on Tuesday, a French security official said Wednesday.
French authorities remain "very cautious" about the information because they receive such notes routinely, the official said.
Belgian officials are cautious too, as the information is believed to be from a single intelligence source and hasn't been confirmed elsewhere.
