Thousands of migrants wait for their departure to Germany at the Austrian side of the Hungarian-Austrian border in Heiligenkreuz on September 19, 2015 as several thousand migrants arrived from Croatia.

German police are investigating an asylum-seeker on suspicion that he fought for ISIS in Syria, newspaper Welt am Sonntag reported Sunday.

The suspect is a Syrian national and lives in an asylum-seeker shelter in the northeast region of Brandenburg, the newspaper reported, quoting security sources.

The man had allegedly told other migrants living in the center that he had fought for the ISIS group and killed people.

His claims were filmed secretly with a mobile telephone by other residents of the shelter, leading to the probe.

Investigators are now trying to determine if the Syrian was indeed a member of the ISIS, the newspaper reported.

A spokeswoman for federal police declined to confirm or deny the report.

Despite the case, federal police do not believe that militants are infiltrating Germany through the influx of refugees.