Three Pakistani men, two of whom are asylum-seekers, are currently under investigation. The third man is a long-term resident of Germany.

The men, who are aged between 28 and 31, were arrested on Sunday and later released for lack of evidence. “There are no grounds to continue to hold them,” a police spokesman said.

There are fears the incidents could cause a backlash against immigrants after it emerged most of victims described their attackers as foreign in appearance.

“The women said that it was their impression the perpetrators were South Asian,” a police spokesman said.