The wife of British hostage Alan Henning has called on "the people of the Islamic State to see it in their hearts to release my husband", describing him as a "peaceful, selfless man".
Mr Henning, a former taxi driver from Manchester, was kidnapped last December in Syria by Islamic State (IS) militants.
The 47-year-old aid worker was shown at the end of a video last week after the beheading of fellow British captive David Haines.
Alan Henning's wife called him a 'peaceful, selfless man'
Mr Henning's wife Barbara said she has sent messages to IS asking them to release her husband but has had no response.
In a statement released through the Foreign Office she said: "Alan is a peaceful, selfless man who left his family and his job as a taxi driver in the UK to drive in a convoy all the way to Syria with his Muslim colleagues and friends to help those most in need.
"When he was taken he was driving an ambulance full of food and water to be handed out to anyone in need.
"His purpose for being there was no more and no less. This was an act of sheer compassion.
"I cannot see how it could assist any State's cause to allow the world to see a man like Alan dying."
It is the first time Mr Henning's family has issued a public statement since he was threatened in the IS video earlier this month.
The extremist group has previously released footage showing the killing of American journalists James Foley and Steven Sotloff.
A separate video released this week showed British photojournalist John Cantlie sitting at a desk reading from a prepared script and explaining that he would speak about IS in future videos. There was no threat to kill Mr Cantlie made on camera.
A series of pleas for the release of Mr Henning have been made by high-profile Muslim leaders in recent days, warning IS that the killings and threats are against Sharia law.
Renowned Jihadi ideologue Muhammed al-Maqdisi and the family of jailed Pakistani scientist Dr Aafia Siddiqui, nicknamed "Lady al Qaida", whose release has been demanded by IS extremists, have also called for Mr Henning to be freed.
Turkey announced yesterday that 49 of its nationals who had been seized by IS in Iraq have been released and safely returned to their country.
The hostages were taken from the Turkish consulate in Mosul, Iraq on June 11, when the IS militants overran the city.
A Foreign Office spokesman said: "The Turkish hostages' safe return home is welcome news for their family and friends and for Turkey.
"The UK condemns the practice of hostage-taking, which is a terrible threat to the nationals of all countries."
Barbara Henning's statement in full:
"I am Barbara Henning the wife of Alan Henning.
"Alan was taken prisoner last December and is being held by the Islamic State.
"Alan is a peaceful, selfless man who left his family and his job as a taxi driver in the UK to drive in a convoy all the way to Syria with his Muslim colleagues and friends to help those most in need.
"When he was taken he was driving an ambulance full of food and water to be handed out to anyone in need.
"His purpose for being there was no more and no less. This was an act of sheer compassion.
"I cannot see how it could assist any State's cause to allow the world to see a man like Alan dying.
"I have been trying to communicate with the Islamic State and the people holding Alan. I have sent some really important messages but they have not been responded to.
"I pray that the people holding Alan respond to my messages and contact me before it is too late.
"When they hear this message I implore the people of the Islamic State to see it in their hearts to release my husband Alan Henning."