German authorities say a man suspected of having worked for the Islamic State group has been arrested at a refugee accommodation center.

The Dortmund prosecutor's office said the 31-year-old was arrested in the western town of Unna on Thursday, news agency dpa reported. It stressed that the investigation is at a very early stage.

The Bild newspaper had previously reported on the arrest. Without citing sources, it said the man came from Syria and that anti-IS activists from that country had posted pictures of the suspect online.

Germany has seen around a million refugees and other migrants arrive this year.