The investigation into one of them has revealed he had links to a network of people that were involved in a gunman's thwarted August 2015 attack on a Paris-bound train.
Information gathered so far seems to indicate that the three -- arrested in the northern state of Schleswig-Holstein by special police forces -- were brought to Europe by the same organization of smugglers that imported the Paris attackers, German Interior Minister Thomas de Maiziere said in Berlin.
Their travel documents also appear to have originated from the same forger, de Maiziere said.
The three -- two Syrian teenagers and one man in his 20s, identified as Mohamed A. -- came to Germany in the middle of November 2015 via Turkey and Greece, the German Federal Prosecutor's Office said.
The suspects were arrested when 200 police and security officers raided six locations, including three refugee shelters. The 17-year-old had been trained in handling weapons and explosives in Raqqa, IS's stronghold in Syria, prosecutors said.
They received fake passports, mobile phones loaded with a pre-installed communication programme and four-figure cash sums in US dollars. At a news conference, Mr de Maiziere said they were trafficked into Europe by the same organisation that supported the three men who blew themselves up outside the Stade de France national football stadium in Paris on 13 November last year.
