European counterterrorism agencies scrambled Friday to asses the potential danger of a complex and growing terrorism threat exposed by the arrests of more than a dozen people with suspected links to Islamic extremists.
As many as 20 sleeper cells of between 120 and 180 people could be ready to strike in France, Germany, Belgium and the Netherlands, a Western intelligence source told CNN.
European Union and Middle East intelligence agencies had identified an “imminent threat” to Belgium, and possibly also to the Netherlands, the source told CNN national correspondent Deborah Feyerick.
Intelligence officials in Europe were trying to determine the nature of the wider threat, a senior European counterterrorism official told CNN. They were monitoring several groups of men who have returned from fighting in Syria.
It is believed ISIS directed the men to return to Europe to launch attacks in retaliation for airstrikes against the terror group in Syria and Iraq, according to the official.