Police in Germany have opened investigations into 40 alleged extremists who have entered the country posing as refugees, according to information obtained by regional daily Neue Osnabruueker Zeiting.
In 2015 more than a million refugees and immigrants entered Germany, with police receiving 369 tip-offs that immigrants were members of or supported terrorist organisations.
Federal investigators have uncovered enough evidence to pursue 40 of these allegations, according to the report, with suspects under investigation for offences including membership of terrorist groups and planning terror attacks.
"More attacks by Islamist terrorist cells cannot be ruled out," German federal police told the publication.
In January, two men were arrested at a refugee centre in Berlin and the western town of Attendorn for allegedly planning terror attacks in the German capital.
The German Interior Ministry cautioned that many of the leads had come from other asylum seekers pursuing vendettas against fellow refugees, or from members of far right organisations seeking to smear refugees as terrorists.
Wolfgang Bosbach, an MP for Angela Merkel's Christian Democratic Union (CDU), warned of the dangers posed by refugees without valid identification entering the country, claiming that as many as many as 60% of those arriving in Germany in recent months did not have passports.
"The dangers that arise from this must be taken very very seriously - that is something that the attacks in Brussels and Paris have made clear to us," cautioned Bosbach.
Germany's official parliamentary opposition, the Left party, warned of the dangers of anti-refugee prejudice.
"The possibility that individual IS-members - including trained assassins - could be among refugees mustn't lead to asylum seekers from Syria and Iraq generally being suspected of terrorism," said the party's interior affairs spokeswoman Ulla Jelpke.