The series of counter-terror raids conducted by Belgian law enforcement last night across the country served to neutralize a network of up to 20 sleeper cells operating in Belgium, France, Germany, and the Netherlands, according to a source speaking to CNN.

The “Western Intelligence source” told the network that an estimated 120 to 180 people are part of the group attacked last night. Other sources within Belgian law enforcement told CNN that the cells were in part formed by individuals returning from Syria and Iraq and receiving instructions on how to operate from the Islamic State terrorist organization.

Authorities in Belgium announced late last night that they had conducted a series of raids on the homes and headquarters of individuals believed to be planning an “imminent” attack on the nation. The largest raid, in an apartment above a bakery in Verviers, resulted in the deaths of two suspects and one injury. All three had recently returned from Syria; authorities estimate that up to 300 Belgian citizens have traveled there to join the Islamic State. Thirteen others were arrested in raids on locales across Belgium. The raids and reported size of the sleeper cells highlight the growing danger of Islamic enclaves or “no-go zones” in which Islamic communities have begun imposing Sharia law– a danger not just to Belgium, but all of Europe.

Authorities also told the press that they were investigating links between one of the suspects arrested last night and Amedy Coulibaly, the French jihadist who attacked  Kosher deli in Paris last Friday in an attempt to help Said and Cherif Kouachi, the brothers responsible for the terrorist attack on satirical magazine Charlie Hebdo. Coulibaly pledged his allegiance to the Islamic State in an online video.

Reuters reports that, in addition to finding the suspects home, police found in apartment in Verviers “police uniforms, explosives and guns including four AK-47 assault rifles,” corroborating evidence that the suspects were plotting an imminent attack in Belgium. In addition to those detained in Belgium, France has detained three suspects the Belgian government requested to place into custody for questioning.

While news of the raids spread quickly last night thanks to law enforcement leaders holding a press conference, actual footage of the event only began to trickle out slowly to the public thanks to witnesses armed with camera phones. Video and photos surfaced on social media late last night showing police storming the Verviers bakery building. Local media also published video, apparently taken from across the street of the building, showing police forcefully entering the premises.

Estimates on how many European nations are fighting in Syria and Iraq on behalf of the Islamic State are in the thousands, with the European Union estimating in September that 3,000 citizens, including children, had left Europe to restart their lives in the Islamic State (those numbers have increased significantly since then). Both European Union and individual state officials have expressed profound concern that those who have left to receive training from the terrorist group will return to the countries of their citizenship and engage in more terrorist activity.