The current system of automatic early release for prisoners serving more than four years in jail is to come to an end.

First Minister Nicola Sturgeon announced that no long-term prisoner in Scotland will be eligible for automatic release after serving two-thirds of a sentence.

The Prisoners (Control of Release) (Scotland) Bill, which is currently making its way through Parliament, previously proposed an end to automatic early release for sex offenders given a jail sentence of four years or more and others who have been ordered to spend a minimum of 10 years behind bars.

But Ms Sturgeon confirmed today that the provisions would be tightened to ensure that no prisoners serving four years or more for serious offences would be automatically released on licence after two-thirds of their sentence.

Experts have raised concerns about prisoners being released ''cold'' after serving all of their sentence in prison, rather than spending some of it supervised on licence in the community.

However, the First Minister also announced a guaranteed period of supervision would be put in place for prisoners guilty of serious offences coming out of custody into the community.

She said: "The safety of the public is an absolute priority of this Government, and we have made significant progress in recent years, with an additional 1,000 police officers on our streets and recorded crime now at its lowest level in 40 years.

"But we are not complacent, and we recognise that tough action is required to tackle those offenders who commit the most serious crimes, ensuring that communities are kept safe while at the same time making efforts to reduce the likelihood of reoffending.

"Prison remains the most appropriate place for serious offenders, and we had already included proposals in the Prisoners (Control of Release) Bill to end automatic early release for certain categories of prisoner.

"Today I am announcing that we will go much further, ending automatic early release at two-thirds of their sentence for all long-term prisoners in Scotland - which are defined as those sentenced to four years or more. That means every prisoner serving a sentence of four years or more will remain in jail for much longer than is currently the case if deemed necessary by the Parole Board.

"As an additional safety measure, I can also confirm today that we will introduce a guaranteed period of supervision for these long term prisoners, to be set out as part of their sentence, which will aid their rehabilitation and help them reintegrate into communities."

She added: "This is a concrete example of the Scottish Government delivering on our justice commitments - indeed, with today's announcement we are going significantly further in ending automatic early release than our initial legislation had proposed."

Susan Gallagher, acting chief executive of Victim Support Scotland, said: "For those who live in all of the communities in which we work this should be viewed as a step closer to achieving a system in which sentences are straight-forward and understandable to the victim and those communities.

"We also support the guarantee of a period of post-release supervision for prisoners, as we recognise the significant role played by community supervision, not only in facilitating enhanced reintegration into the community but also in supporting offenders to desist from further offending."

The Scottish Conservatives said the move is a "step in the right direction", but there is still a "long way to go".

The party's chief whip John Lamont said: "This is clearly welcome news but it still falls short of what the SNP has been promising to do since first getting elected in 2007. It will still mean that 97% of prisoners will be automatically released from prison half way through their sentence, no questions asked.

"Automatic early release of prisoners is an insult to victims and makes a mockery of our justice system. Despite the announcement today, the vast majority of offenders will continue to enjoy the benefits of our soft touch justice system."

SNP MSP Christian Allard said: "Today's welcome announcement will mean that the most serious offenders in Scotland will remain in prison for longer than would otherwise be the case - helping to protect the public and keep communities safe.

"By strengthening the legislation in this way, we are taking the tough action that is needed when it comes to those found guilty of serious crimes."