London (AFP) - The wife of a British taxi driver held by Islamic State jihadists renewed her appeal on Tuesday for her husband's release, saying that his captors were ignoring the "verdict of their own justice system".

Barbara Henning said that her husband Alan, who left the family home near Manchester in northern England to deliver aid to victims of Syria's civil war, had been "in the right place doing the right thing."

"We have not abandoned Alan and we continue in our attempts to communicate with you," she said in a statement.

"I have had no contact from Islamic State holding Alan other than an audio file of him pleading for his life."

The family of the 47-year-old humanitarian worker had been "given so much hope by the outcry across the world," she revealed.

Mrs Henning claimed that Muslims globally were criticising IS over her husband's treatment and accused the militant group of disregarding the "verdict of their own justice system" after claiming that a Sharia court had found him "innocent of being a spy".

She called on IS leaders to "open their hearts and minds to the truth about Alan's humanitarian motives for going to Syria".

"Surely those who wish to be seen as a state will act in a statesmanlike way by showing mercy," she added.

When asked to give a message to her husband, Henning said: "We miss you and we're dreadfully concerned for your safety. We need him back home. Thank you."

Henning volunteered to help drive an aid convoy to Syria for Muslim charity Aid4Syria and was kidnapped 10 months ago.

It is the family's third appeal since Henning, a father of two teenage children, was threatened in a video that showed the brutal killing of British aid worker David Haines earlier this month.