Two youths of 17 and one of 14 have been arrested in connection with a string of group rapes in Rotterdam, city police said on Tuesday.

The victims were aged 12 and 16 and were all pupils at the Lentiz Life College, a trade school on the border between Rotterdam and Schiedam. The assaults took place in cellars and sheds in the west of the port city, police said.

The police statement did not say how many girls had been attacked but said the investigation was started after one girl made a formal complaint.

‘It was a long and difficult investigation,’ detective Lincy Lansbergen said. ‘We quickly realised there was more than one victim. We knew the signs but we did not have the statements. Some girls preferred to talk to their parents than to us, for a variety of reasons.’

Lansbergen said the girls who had been attacked are a vulnerable, insecure group who were often charmed by their attackers. ‘The case is made more difficult because to a certain extent the girls liked the boys and were willing to go with them,’ she said.

‘They like to hang out with them, but that does not give the boys the right to abuse them… we want to make it clear to the girls that they can set the boundaries and the boys should respect them.’

The investigation is still underway and the police are appealing for more girls who may have been victims of the gang to come forward.