The wife of British aid convoy volunteer Alan Henning has issued a statement to the Islamic State calling on his captors to release him.
Mr Henning, 47, a former taxi driver from Manchester, was captured last December near the town of al Dana in Syria by IS militants.
He was shown at the end of a video last week following the murder of fellow British captive David Haines.
The statement, issued through the Foreign Office, said: "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.Mr Henning (L) had driven an ambulance full of food and water to Syria
"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 Islamic State to see it in their hearts to release my husband Alan Henning."
It is the first public statement by Mr Henning's family since he appeared in the IS video.
It follows an appeal by Muslim scholars in the UK calling for the release of the Briton, who was captured in December near the town of al Dana.
IS has previously released footage showing the murders of US journalists James Foley and Steven Sotloff.
A separate video last week showed British photojournalist John Cantlie, dressed in an orange jumpsuit, saying he wanted to "convey some facts" about IS and saying he would speak about the group in future videos. There was no threat to kill Mr Cantlie in the video.