An Iranian asylum seeker at the Perth immigration detention centre says he is being transferred to Christmas Island to cover up an allegation of sexual harassment he made against a Serco employee last week.

Immigration Minister Scott Morrison confirmed earlier this week the Serco employee had been stood down pending an investigation into the incident.

The detainee claimed the Serco staffer asked him several times to perform sexual acts in exchange for a mobile phone, money or extra food.

Mr Morrison has also said the matter had been referred to police.

However, the detainee has told the ABC he had not yet been interviewed by police.

He said he was taken to a meeting with Serco staff yesterday and told he would be transferred to Christmas Island.

He had asked whether he was being sent there to "cover up" the alleged sexual harassment case.

"When I asked my case manager that I need to be in here for an investigation, he told me that I came to Australia after 19th July 2013 and I have to transfer to offshore for processing," the detainee said via social media.

"He told me that they are not trying to cover it up. But I think they do because they already fired the guy and transferring me to offshore - problem solved."

Ticket to Christmas Island 'already booked'

He said he was told his ticket was already booked.

"Even one of the Serco managers, who is a nice guy, told me that they fired the guy, and then they are sending me back away, and then that's it," he said.

A spokeswoman for Immigration Minister Scott Morrison issued a brief statement in response to the claims.

"If an individual is transferred to another part of the detention network, it has no impact on any ongoing police investigation," she said.

"The [Immigration] Department will ensure individuals are made available to police as and when required to further any enquiries they may have."

The detainee spent time in Malaysia before taking a boat to Australia.

He arrived after July 2013, meaning any asylum claim is processed offshore.

He was initially sent to the Christmas Island detention centre but then transferred to Perth for health reasons.

The detainee said his case manager told him the police investigation into the alleged sexual harassment would start next week.

"He promised me that the investigation will continue because it is already in the media and police," he said.

The AFP said it was evaluating a referral on the matter.

In the UK, police have investigated unproven claims by a 29-year-old Pakistani woman that she was sexually assaulted by a male Serco employee.

Keith Vaz, chair of the Home Affairs Select Committee, reportedly said this week that senior Serco officials would be called to UK parliament next month to answer questions.