German police have arrested three Syrian nationals suspected of being sent to the country by Islamic State (Isis), prosecutors have revealed.
The three men, aged between 17 and 26, were held at refugee centres in Schleswig Holstein and Lower Saxony, Welt reported. Mobile phones, hard drives and documents were seized in the raids, which involved the GSG9 specialist anti-terror unit.
The men are suspected of having been sent to the country in November 2015, "either to carry out a mission that they had been informed about or to wait for further instructions", prosecutors declared in a statement, reported Reuters.
"Concrete missions or orders have not so far been found in the course of investigations carried out so far."
German Interior Minister Thomas de Maziere said at a press conference the men may have had links with the Isis cell which carried out the Paris attacks in November 2015, in which 130 people were killed.
The three – named only as Mahir al-H, 17, Ibrahim M, 18, and Mohamed A, 26 – are believed to have travelled through Turkey and Greece using false passports, prosecutors said.
They are believed to have volunteered for the alleged mission, and Mahir al-H is thought to have received weapons and explosives training in Isis' Iraqi stronghold, Mosul.
The trio allegedly received fake passports, mobile phones fitted with a pre-installed communications programme, and four figure cash sums in US dollars before embarking for Europe.
De Maziere said that they were trafficked into Europe by the same organisation that smuggled in the men who blew themselves up outside Paris' Stade de France on 13 November. Their passports were made in the same workshop as those of the Paris attackers, and the three "could have been a sleeper cell", de Maziere said.
Investigators placed the men under surveillance after receiving a tip-off from Germany's domestic intelligence agency, the BfV, reported German press agency DPA.
In July, a 17-year-old Afghan refugee injured several people in a knife and axe attack on a train in Wurzburg, Bavaria. Days later a 27-year-old Syrian refugee detonated a suicide bomb near a music festival in Ansbach, Bavaria, injuring 12.
In videos released by IS after their deaths, both attackers had pledged allegiance to the group.
In May, German media reported that police had received nearly 400 tip-offs about terrorists posing as refugees, with 40 cases under active investigation.
Following the attacks there has been a decline in support for Chancellor Angela Merkel's government and its policy of welcoming refugees into the country.