Isla Bryson, a transgender woman found guilty of raping two women before transitioning, will not be imprisoned in Scotland’s all-female Cornton Vale prison, Nicola Sturgeon has told the Scottish parliament.

The first minister confirmed Bryson would not be incarcerated in the women’s prison “either short-term or long-term”, after news the offender had been transferred there on Tuesday prior to sentencing prompted outrage across the political and campaigning spectrum.

Pressed repeatedly on the matter at first minister’s questions on Thursday by the Scottish Conservative leader, Douglas Ross, Sturgeon said she agreed it was not possible to have a rapist incarcerated within a female prison.

Stressing this was an operational matter for the Scottish Prison Service (SPS), she added: “The Scottish Prison Service is in the process of giving effect to the decision it has taken not to incarcerate this prisoner in Cornton Vale” and that she expected the prisoner to be moved within 72 hours.

On Tuesday, there was widespread anger that Bryson – who first appeared in court in 2019 as Adam Graham and was known to both victims by that name – was being remanded in a female prison.

The Guardian understands the offender was being kept in segregation while an initial case conference was undertaken on Tuesday, involving SPS staff, with NHS and psychological input and an equality and diversity officer, in order to assess the risks and consider longer-term placement.

Opponents of the Scottish government’s gender recognition reforms – which the UK government has blocked from going for royal assent because of “safety issues for women and children” – said the case vindicated their concerns about a lack of safeguards in the bill.

Asked directly by Ross if it was safe for female prisoners to be in the same facility as a double rapist, Sturgeon responded: “Firstly, in general, any prisoner who poses a risk of sexual offending is segregated from other prisoners, including during any period of risk assessment.

“Secondly, there is no automatic right for a trans woman convicted of a crime to serve their sentence in a female prison, even if they have a gender recognition certificate. Every case is subjected to rigorous individual risk assessment and as part of that the safety of other prisoners is paramount.

“Finally, in general terms and perhaps most importantly, I heard the chief executive of Rape Crisis Scotland say yesterday: ‘I don’t see how it’s possible to have a rapist within a female prison’. And so let me be very clear, I agree with that statement”.

But Sturgeon also underlined that it was important during such exchanges “that we do not even inadvertently suggest that somehow trans women pose an inherent threat to women. Predatory men, as has always been the case, are the risk to women. However, as with any group in society, a small number of trans people will offend and where that relates to sexual offending, public concern is understandable”.

Bryson, from Clydebank, West Dunbartonshire, was found guilty of two charges of rape on Tuesday after a six-day trial at the high court in Glasgow.

The jury heard Bryson raped two women – one in Clydebank in 2016 and one in Drumchapel, Glasgow, in 2019 – after meeting them online. Prosecutors described Bryson as “preying” on vulnerable women.