The charity which employs British IS hostage David Haines has said it is “deeply shocked” by the terrorist video of him broadcast this week and called for his immediate release.
ACTED said that the threats made to the Scotsman’s life were “intolerable”.
Haines, 44, was taken while working for ACTED in Syria in March 2013, having previously helped local people in Libya and South Sudan.
In a statement the charity said: “ACTED strongly condemns the violence and threats against David.
“A man’s life should never be threatened on account of his humanitarian commitment.”
In its statement, ACTED 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.
It added: “ACTED is deeply shocked by the images broadcast earlier this week. The threats on David Haines’ life are intolerable.
“We have been mobilised from day one with David’s family. More than ever, we are pursuing our efforts, and our thoughts are with David and his family.”
Militants from Islamic State – also referred to as Isil or Isis – have threatened to kill Mr Haines, who they are believed to be holding in Syria.
They have already beheaded two American journalists, posting the evidence on line in gruesome videos featuring a masked jihadist with a British accent.
Mr Haines has 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 secondary school, he has worked for aid agencies in some of the world’s worst trouble spots.
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.
In 2012 Mr Haines worked in South Sudan for the Brussels-based charity Nonviolent Peaceforce, which sends unarmed civilian peacekeepers to conflict zones.
In a statement it said he acted as a “non-partisan unarmed civilian peace facilitator” in the fledgling African state.
“We join with people around the world in pleas, thoughts and calls for his safe release,” it said.