Greek police detained four people on Saturday over alleged links to an Islamist cell in Belgium, where two suspected terrorists were shot by officers on Thursday.

One of the men, aged 27 is alleged to have been in regular contact with the cell in the Belgian town of Verviers, where two extremists were killed and one arrested.

Sources said that Greek police acted after a request from Interpol. Belgian authorities found that members of the Islamist cell in Verviers called a contact in Greece regularly.

Greek officers were given the identity of the man, who, like the three suspects in the Belgian raid, had recently returned from fighting in Syria. Reports in Belgium suggest that the suspect in Greece was the brother of one of the alleged extremists and had been coordinating the group’s movements. One TV channel, VTM, reported that he is of Algerian descent.

Sources also revealed that in November, Greek authorities were asked by their French counterparts to interview three families who had tried to travel together from France to Syria to fight in the civil war. The 16 people were questioned for 12 hours by Greek police, who also searched their cars. Nothing suspicious was found and they were escorted to board a ferry bound for Italy.