Female detainees at Yarl's Wood immigration centre made six allegations of sexual assault against staff in a three-year period, it has emerged.
The assaults were said to have taken place between 2013 and 2015 at the Serco-run centre in Bedfordshire.
Home Office minister James Brokenshire said two further allegations were made at other immigration removal centres.
Serco said there were no proven cases of sexual abuse at the centre in the last three years.
Both the Home Office and Bedfordshire Police said they could not provide details of the outcome of the investigations, but Mr Brokenshire said all allegations were investigated.
Mr Brokenshire said: "Of these six allegations, one was made in 2013, three in 2014 and two in 2015."
Founder of Women for Refugee Women, Natasha Walter, said the claims were "really, really troubling".
"The women who are locked up in Yarl's Wood... the majority are survivors of serious sexual violence and often torture in their countries of origin."
She called on the new Home Secretary Amber Rudd to stop holding women who have sought asylum in detention centres.
Yarl's Wood, which holds more than 350 detainees, most of whom are women, was recently criticised for a lack of staff training.
Conservative MP David Burrowes, who is the vice-chairman of the All-Party Parliamentary Group on Refugees, said: "There is a need for greater transparency and openness at Yarl's Wood."
MPs are planning to visit the centre, following criticisms of the way it is run.
A spokesman for Serco said it "takes any allegation of sexual abuse extremely seriously" and complaints are referred with "no exceptions" to the Home Office and the police.
He added: "There have been no incidents of sexual abuse at Yarl's Wood in the last three years."