British Muslim leaders have called for the immediate release of Alan Henning, the UK hostage threatened with death by Islamic State (IS) extremists in Syria.

In a letter in the Independent, they described IS as un-Islamic fanatics and urged them to show mercy on Henning.

The 47-year-old was a volunteer on an aid convoy in December 2013 when he was seized just after crossing into Syria.

The letter said anyone undertaking a humanitarian act should be held in the highest esteem.

This was in contrast, they said, to the “senseless kidnapping, murder and now despicable threats to Henning at the hands of so-called ‘Muslims’”.

They said such actions could not be justified anywhere in the Koran or Islamic tradition, and the “fanatics” were not acting as Muslims but perpetrating the worst crimes against humanity.

More than 100 British Muslim imams, organisations and individuals wrote to express their “horror and revulsion” at the “senseless murder” of Briton David Haines and the threat to the life of Henning.

They said Henning was a volunteer who travelled to Syria to help civilians.

The letter cited verses from the Koran against killing, and appealed to the kidnappers to release Henning immediately, reports the BBC.

Its signatories insisted that British Muslim communities would continue to do everything within their power to prevent more young men or women getting caught up in Islamic State’s “poisonous ideology”.