A SENIOR German security official has revealed that counter-terrorist services are trying to track hundreds of sleeper cells and hit squads sneaked into the country among refugees.
Mr Hasuer said: "The risk is abstract. But it’s very high.
"We have to accept that we have hit squads and sleeper cells in Germany.
"We have substantial reports that among the refugees are hit squads."
He said his agents were investigating hundreds of reports, some from refugees themselves, that ISIS was sending teams into the country.
He added: "We have irrefutable evidence that there is an ISIS command structure that makes an attack in Germany very likely."
Last month, 15 people were injured when a Syrian asylum seeker blew himself up at a music festival in Ansbach.
Following this, another man attacked passengers on a train with an axe.
Both of these attacks were found to have been inspired by ISIS.
Following other terrorist incidents in France and Belgium, Germany has now laid out a security crackdown to wipe out the Islamist terror threat.
Among a range of new anti-terror plans announced today, the German Interior Minister will propose swifter deportation of foreign criminals.
Thomas de Maiziere is also expected to call for greater use of video surveillance and powers to investigate suspects as young as 14.
There are also plans to ban public wearing of the burka and radical Islamist funding of mosques as well as to ease medical confidentiality for mentally unstable individuals.
The German defence minister Ursula von der Leyen has also said it is time to call in the army.
She wants the armed forces on the streets alongside police in the event of a terror attack.
The measures come as German police detained a Syrian refugee on Wednesday.
The man, taken from a refugee centre in Dusseldorf, was suspected to have fought with ISIS
German authorities also carried out separate raids against three suspected Islamic State sympathizers.
The local police reporter said they were "handling even vague leads with the utmost rigour."