Leder for det tyske Overvåkingspoliti, Hans-Georg Maassen, sier den islamske staten sender krigere ind i Europa forklædt som migranter eller flygtninge.
Tysk politi arresterede to personer på et asylmottak i Berlin torsdag, mistænkt for å ha planlagt et terrorangreb.
Hans-Georg Maassen said the terrorist attacks in Paris last November had shown that Islamic State was deliberately planting terrorists among the refugees flowing into 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.
Tysk politi har mottatt over 100 tips om asylsøgere som kan være terrorister.
“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 said.