Scotland's prison authorities have been asked to release "a limited number" of prisoners early due to the coronavirus pandemic, MSPs have been told.
Justice Secretary Humza Yousaf said jails were under pressure due to a "significant" number of staff being off and concerns about health and safety.
Some prisoners on short sentences with less than three months to serve will now be eligible to be released early.
Mr Yousaf said this was a "necessary and proportionate response".
He said action was needed now with the lockdown having been extended for another three weeks.
Ministers were given the power to release some prisoners early in emergency legislation passed at Holyrood earlier in April.
In an update to MSPs at Holyrood, Mr Yousaf said 89 prisoners were currently in isolation due to the virus, saying "they are being monitored accordingly".
He said there is also "a significant number of prison staff who cannot be in work", which taken together with a ban on visits was making prison "an especially challenging environment at present".
He said: "After careful consideration and in agreement with the views of the chief executive of the Scottish Prison Service (SPS), I will be asking the SPS to consider the release of a limited number of short-sentenced prisoners towards the end of their time in custody. I believe this is a necessary and proportionate response to the current situation in our prisons.
"This is in the interests of maintaining security and good order in our prisons and vitally also in safeguarding the health, safety and welfare of prisoners and those working in our prisons. This action will help give the SPS sufficient capacity, including increased single-cell occupancy, to continue to maintain a safe custodial environment."
Mr Yousaf said prisoners on sentences of 18 months or less, who are in the last three months of their time in custody, would be considered for release.
About 450 prisoners fall into this category, and Mr Yousaf said the release process would begin at the end of the month.
But anyone convicted of sexual offences, domestic abuse or terrorism or who would be subject to a supervision order would not be considered for release.
Conservative MSP Liam Kerr said victims of crime would be "very concerned" by the move, but it was welcomed by Labour's James Kelly as a "correct and appropriate" response.