“An investigation has been launched after a report was made to police involving concern for the welfare of a small group of teenage girls within the grounds of the Islamic School for Girls in Lancaster," the police said in a statement.
A 40-year-old man from Bolton and a 30-year-old man from Blackburn have been arrested on suspicion of sexual assault and false imprisonment and a 53-year-old man from Blackburn has been arrested on suspicion of false imprisonment.
The school is takes up the grounds of the old Royal Albert Hopsital.
“We are still at the very early stages of the investigation and our aim at the moment is to respond to the concerns raised proportionately, in a measured way and with sensitivity," say police.
“Searches at the school are being conducted by specialist, female officers with sensitivity and are being carried out as quickly as possible to ensure minimum impact.
“We are working closely with the school and the local authorities to establish the circumstances around exactly what has taken place and we have specialist officers supporting the victims.”
"The school is aware of the allegations that have been made and at the present moment the school is fully co-operating with the police with their investigations into the matter," the School has said in its own statement.
"The school will publish a statement of any details it receives, once this has been received.
"We expect the matter to be cleared up soon."