On Thursday, the Belgian federal police conducted a raid in Verviers city as part of a wider anti-terrorist operation.

In the Netherlands, a man from Tajikistan and his wife were arrested, suspected of belonging to the self-proclaimed Islamic State (IS).

The suspects are linked to several residences in Germany where seven IS-linked suspects have been arrested. The National Coordinator for Security and Counter-Terrorism (NCTV) in the Netherlands said there are growing signals that jihadist organizations are preparing to carry out terrorist attacks in Europe.

According to the group's latest report, released in late May, the threat comes mainly from IS-controlled networks in Syria and Afghanistan.

In a threat assessment published last month, Belgium's Coordination Unit for Threat Assessment (OCAM) warned that the IS propaganda machine and its roots in Afghanistan are working at maximum capacity to incite extremist attacks.