Media playback is unsupported on your device Media caption Alan Henning was seized in Syria in December

The family of British hostage Alan Henning has received an audio file of him "pleading for his life".

Details of the message have not been released, but Mr Henning's wife Barbara issued a message in response calling on Islamic State (IS) to release him.

Mr Henning, a taxi driver from Eccles in Salford, was delivering aid when he was captured in Syria in December.

Meanwhile UK authorities have said they are "getting warm" in their hunt for a militant seen in IS beheading videos.

IS films have showed the beheadings of two Americans and one Briton in recent weeks, and a militant in the videos seems to speak with a British accent.

Britain's Foreign Secretary Philip Hammond told US network CNN: "There's a big investigation and we are getting warm.

"We are narrowing down the field but I don't want to say any more at this stage."

'Loud and clear'

In a statement issued through the Foreign Office, Mrs Henning said: "I and people representing me continue to reach out to those holding Alan.

"Islamic State continue to ignore our pleas to open dialogue.

"I have seen Muslims across the globe question Islamic State over Alan's fate. The voices of the people have spoken out loud and clear.

"He was working with Muslims to help the most vulnerable within Syria. Nothing has changed. He went to Syria to help his Muslim friends deliver much needed aid.

The statement, the second released by the Henning family in recent days, continued: "We are at a loss why those leading Islamic State cannot open their hearts and minds to the facts surrounding Alan's imprisonment and why they continue to threaten his life.

"I have been told that he has been to a Sharia court and found innocent of being a spy and declared to be no threat. I implore Islamic State to abide by the decisions of their own justice system.

"Please release Alan."

Death threat

Mrs Henning first spoke out at the weekend, saying she had sent messages to IS but had received no response.

Last week, British Muslim leaders called for Mr Henning's immediate release in a letter in the Independent newspaper.

IS militants issued a threat to kill Mr Henning in a video released on 13 September which showed the killing of another British man, David Haines.

His death followed those of two US hostages, journalists James Foley and Steven Sotloff, both of which were also shown in videos.

Earlier on Tuesday IS released a second video of UK journalist John Cantlie, who was kidnapped in Syria in 2012 and is being held hostage.

Like the first video, which was posted online less than a week ago, Mr Cantlie is shown speaking to the camera about IS and saying he has been abandoned by the UK government.