Three Syrian men believed to have been sent to Germany last year by the Islamic State group as a possible “sleeper cell” were arrested in raids on Tuesday, part of efforts to root out extremists sent to Europe amid the migrant influx, authorities said.

The three are accused of coming to Germany in mid-November at the behest of IS “in order either to carry out an assignment they had already received or to keep themselves ready for further instructions,” federal prosecutors said. The three are suspected of membership in a foreign terrorist organization.

Their arrests followed raids at refugee homes in Schleswig-Holstein, Germany’s northernmost state. Interior Minister Thomas de Maiziere said the men had been under observation for months, and that “there are no indications of concrete attack plans” at present.

“This may have been a sleeper cell,” he told reporters.

De Maiziere said the suspects appear to have made it to Europe through the same channels as two men who blew themselves up outside France’s national stadium in November in the Paris attacks claimed by IS.

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Image courtesy of Uli Deck/dpa via AP