Searches are continuing within the grounds of an Islamic school for girls as police investigate claims of sexual assault and false imprisonment.
Police were informed at the weekend of an alleged incident involving "a small number of teenage girls" at Jamea Al Kauthar school in Lancaster last Tuesday.
The report made on Saturday was said to have raised concerns over the welfare of the girls.
Detectives executed a search warrant of the premises last night and also arrested three men at the site.
Two of the men are being interviewed on suspicion of sexual assault and false imprisonment. A third man from Blackburn is being questioned on suspicion of false imprisonment.
Police would not comment on whether they were members of teaching staff but it is understood they are linked to the school.
Bosses at Jamea Al Kauthar said they were co-operating with what police labelled a "complex investigation" and added it anticipated the matter would be "cleared up soon".
Superintendent Andy Webster said officers were currently focused on the one alleged incident and they were trying to ascertain whether the report related to existing or former pupils of the school.
He said: "We are still at the very early stages of what is a complex investigation and we have dedicated officers working to establish the full facts.
"Our aim at this stage is to respond to the information given to us in a proportionate and sensitive way.
"We will seek to minimise the impact and the disruption to the school and our local communities while we investigate the allegation."
He said pupils at the boarding school came from across the UK, along with a "significant number" of international students.
"We understand there will be concern from families, both in the UK and abroad," he said.
"In order to make it easier for them to contact us, a dedicated phone line has been set up."
The helpline number for parents in the UK is 0800 092 0410, while those from outside the UK can ring 0207 158 0124.
In a statement on its website, Jamea Al Kauthar said: "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 will publish a statement of any details it receives, once this has been received. We expect the matter to be cleared up soon."
The school is said to be operating as normal as the searches continue within the vast grounds of the former Royal Albert Hospital.
According to its website, the independent boarding school aims to educate Muslim girls over the age of 11 "in a safe, secure, happy and Islamic environment".
Jamea Al Kauthar started with 60 girls in September 1996 and presently caters for 440 residential girls from all over the world on an admission policy of selection by ability, it says.
It continues: "We provide an opportunity to study the traditional sciences concurrently with secondary and further education.
"Jamea Al Kauthar also offers the 'Tahfeez Ul Quraan' programme (committing the whole Koran to memory) and a two-year abridged version of the Islamic Teaching programme in the English medium.
"There are currently 401 girls on roll, of whom around half are above compulsory school age. These older students attend Islamic theology courses each morning and other courses provided by Preston Sixth Form College in the afternoon."
The website said the school grounds comprise a boarding house, the school buildings and a madrassa where the Islamic curriculum is taught.