The wife of a British aid worker held hostage in Syria by the Islamic State group has received an audio message from him pleading for his life.

Barbara Henning said she has been told that her husband, Alan, had been to a Sharia court, and that he was found innocent of being a spy.

In a statement issued on her behalf by Britain's Foreign Office on Tuesday, she said: "I implore Islamic State to abide by the decisions of their own justice system. Please release Alan."

The 47-year-old former taxi driver was kidnapped in December in Syria, shortly after crossing into the country from Turkey in an aid convoy.

Barbara Henning stressed that her husband was working with Muslims to help vulnerable people in Syria.