Politicians have condemned the beheading of Scottish aid worker David Haines by Islamic terrorists.
The so-called Islamic State (IS) released a graphic video showing the 44-year-old being murdered by a militant with a knife.
The murderer speaks with a British accent and is believed to be the same man who beheaded US journalists James Foley and Steven Sotloff in recent weeks.
Mr Haines, who lived in Scone before moving abroad, was taken hostage in Syria in March last year.
Prime Minister David Cameron said: “This is a despicable and appalling murder of an innocent aid worker. It is an act of pure evil.
“My heart goes out to the family of David Haines who have shown extraordinary courage and fortitude throughout this ordeal.
“We will do everything in our power to hunt down these murderers and ensure they face justice, however long it takes.”
Mr Cameron returned to Downing Street shortly after midnight and will chair a meeting of the Government’s emergency Cobra committee on Sunday morning.
First Minister Alex Salmond said the release of the video “has demonstrated a degree of brutality which defies description”, adding:”It should be remembered that Mr Haines was in the region as an aid worker helping local people.
“His murder will be totally condemned by all people with any sense of humanity.
“Our thoughts, sympathies and prayers are with the family members and friends of Mr Haines who have demonstrated both dignity and courage over the past months.”
The news came hours after the family of Mr Haines issued a plea to his captors to contact them.
The Foreign Office said Mr Haines’s family wish to be left alone. A spokeswoman said: “If true this is another disgusting murder. We are offering the family the family every support possible.
“They ask to be left alone at this time.”
Labour leader Ed Miliband said: “I am sickened at the disgusting, barbaric killing of David Haines.
“David Haines was somebody whose only purpose was to help innocent people, themselves victims of conflict.”
Mr Haines had a teenage daughter in Scotland from a previous marriage and a four-year-old daughter in Croatia from his present marriage.
Educated at Perth Academy, he worked for aid agencies in some of the world’s worst trouble spots, including Libya and South Sudan.
He was in Libya during its civil war in 2011, working as head of mission for Handicap International, which helps disabled people in poverty and conflict zones around the world.
Mr Haines was taken hostage while working for ACTED in Syria in March 2013, having previously helped people in Libya and South Sudan.
ACTED has previously said that the threats made to the Scotsman’s life were “intolerable”.
In a statement, it said: “ACTED strongly condemns the violence and threats against David. A man’s life should never be threatened on account of his humanitarian commitment.”
The charity said Mr Haines had worked as “a humanitarian” since 1999, helping people in the Balkans, the Middle East and Africa.
When he was taken by jihadists in Syria he was working to help “tens of thousands of people affected by the crisis” created by the long-running civil war.
Colonel Richard Kemp, former commander of British forces in Afghanistan, said: “Having worked in British Government on hostage rescue I know how much effort has gone in to saving David Haines. Now is the time for retribution.”
Former head of the Army Lord Dannatt said the UK should respond by playing its role in the assault against IS promised by US president Barack Obama.
“What we absolutely need to do is not be cowed in any way by yet another foul murder of a hostage,” he told Sky News.
“But to develop the strategy into a sensible military campaign in coalition with regional players such as Saudi Arabia, Jordan and other countries in the area.
“We can support them to confront, attack and defeat the Islamic State jihadi fighters … and make sure this cancer is removed from the region before it spreads more widely.”