The Department of Immigration has confirmed that 70 asylum seekers detained on Manus Island have been transferred back to detention centres in mainland Australia as part of a plan to empty the regional processing centre as soon as possible to make way for new arrivals under the new transfer deal with the PNG government.

A spokeswoman said the immigration minister, Tony Burke, had signed off the transfer but she was unable to give the date when it had been approved. She said the transfer was “not a knee-jerk reaction” to the allegations broadcast on SBS Dateline on Tuesday. In the TV report a former G4S employee and senior manager at the regional processing facility claimed that some detainees had been raped and abused on Manus and that Department of Immigration staff failed to act to stop further violence.

Burke was heading to PNG on Wednesday and said he intended to investigate the allegations fully.

The spokeswoman confirmed that the group of 70 transferred from Manus were delivered to detention facilities in Darwin earlier on Wednesday and would be dispersed around the detention network on mainland Australia.

The transfer raises questions about which jurisdiction any allegations of assault or rape will fall under, as assaults occurring in PNG should be dealt with by local police.

The department reiterated its statement, issued earlier on Wednesday, that it had received no allegations of rape in the detention facility, and had received one of sexual assault where the alleged victim dropped the charges after being questioned by PNG police.

It is understood that the remaining 60 asylum seekers held in the processing facility will be transferred off the island soon. It is unlikely that asylum seekers who arrived by boat after the government’s 13 August “no advantage” policy announcement will be transferred to Manus. This is because the site is being prepared for those who arrived in Australia following the government’s new deal with PNG that will see all irregular maritime arrivals sent offshore.

It is understood that transfers under the new deal will begin within weeks.