German intelligence officials are aware that ISIS fighters have successfully smuggled in “hit squads” among the flow of Syrian refugees across German borders.

According to Politico, Manfred Hauser — the vice president of BayLfV, the Bavarian region’s intelligence gathering apparatus — told the BBC Thursday that officials must “accept we have hit squads and sleeper cells in Germany.”

“We have substantial reports that among the refugees there are hit squads,” he added. “There are hundreds of these reports, some from refugees themselves.”

Hauser stated that BayLfV is currently following up on the reports of ISIS operatives inside German borders, but maintained the investigation is far from complete.

The CIA has previously warned that ISIS will attempt to exploit both legal and illegal immigration patterns in order to transport fighters to the West.

“ISIL has a large cadre of Western fighters who could potentially serve as operatives for attacks in the West,” Director John Brennan told the Senate Intelligence Committee in June. “And the group is probably exploring a variety of means for infiltrating operatives into the West, including refugee flows, smuggling routes, and legitimate methods of travel.”