First Minister Nicola Sturgeon says she would "feel exactly same" as the family of Paige Doherty after her killer's sentence was reduced.

John Leathem, who killed the 15-year-old- school girl in a "savage and frenzied" knife attack, had his minimum jail term sentence reduced by four years to 23 years following an appeal last week.

The matter was raised at First Minister's Questions on Thursday by Scottish Conservative leader Ruth Davidson.

She asked the First Minister if she agreed with her that it was "entirely unacceptable" for the family to watch their daughter's killer have his sentence reduced on the grounds that his crimes were not as bad as other recent murders.

Leathem's legal team successfully argued that other recent convicted murderers, such as Alexander Pacteau who killed Irish nurse Karen Buckley, were not sentenced to 27 years and therefore his sentence was "excessive and inconsistent comparatively with contemporary sentencing practice".

Sturgeon said: "My heart breaks for the family of Paige Doherty. I met Paige's mother last year and there are, literally, no words to express the pain and grief that she and the rest of her family have gone through.

"Today, I am sure on behalf of everybody in the chamber, I again simply want to put on record my deepest condolences to her for everything she has suffered.

"I have no difficulty whatsoever understanding the sentiments that were expressed by the Justice for Paige campaign.

"If I had been a relative of Paige Doherty, I would have felt exactly the same given the events Ruth Davidson has outlined.

She added: "The only other thing I would say is, being absolutely frank this is the most difficult thing for me to say, this was the decision of an independent judge in a court of law. We have an independent judiciary in this country.

"As well as being First Minister I am a human being and there are many occasions where I look at decisions of courts and wish that different decisions had been reached it may well be that this is one such case.

"But I respect the independence of the judiciary. I do not think anybody in this chamber, and I include Ruth Davidson in this, would expect me to interfere with those decisions but what I can do today is say that I absolutely understand and sympathise with the pain and grief this family is experiencing."

The First Minister's comments come hours after the schoolgirl's parents launched a social media campaign called "#NoJusticeForPaige".

In a statement released through the Justice for Paige group, they said: "Last week's news is an insult to Paige's life, her murder and her legacy and we are not walking away with this decision.

"Tonight we are asking that you take a photo of yourself with a sign saying #nojusticeforpaige and nominate 3 people to do the same and follow the trend.

"We hope to take over social media and show the world, and more importantly - those in the authorities, that we are not accepting this decision and we will fight for Paige's justice until the end."

Scottish Conservative MSP Douglas Ross said he would bring forward a private member's bill to empower judges to set whole life tariffs, ensuring some murderers could never leave prison.

Any such legislation would have to comply with article three of the European Convention on Human Rights, which states: "No one shall be subjected to torture or to inhuman or degrading treatment or punishment".