Hans-Georg Maassen from the Federal Office for the Protection of the Constitution (BfV) gestures during an interview in Berlin, Germany August 4, 2015. REUTERS/Fabrizio Bensch

ISIS has been sending its militants into Europe disguised as refugees, the head of Germany’s domestic intelligence agency (BfV) said on Friday, a day after thwarting a potential ISIS attack in Berlin.

According to Hans-Georg Maassen, the terrorist attacks in Paris last November had revealed that ISIS was deliberately planting terrorists among the refugees pouring to Europe.

“Then we have repeatedly seen that terrorists … have slipped in camouflaged or disguised as refugees. This is a fact that the security agencies are facing,” Maassen told ZDF television.

“We are trying to recognize and identify whether there are still more IS fighters or terrorists from IS that have slipped in,” he added.

Citing Maassen, the Berliner Zeitung newspaper said on Friday that the BfV had received more than 100 warnings that there were ISIS fighters among the refugees currently staying in Germany.

After the Paris attack, Germany’s fears about an attack have grown. German forces arrested on Thursday, two men suspected of being affiliated to ISIS militants preparing an attack in the German capital Berlin.

Furthermore, authorities called off a friendly international soccer match in Hanover last year and closed stations in Munich at New Year as a result of security concerns.

Maassen, however, warned against alarm.

“We are in a serious situation and there is a high risk that there could be an attack. But the security agencies, the intelligence services and the police authorities are very alert and our goal is to minimize the risk as best we can,” he added.