The wife of a British aid worker held hostage in Syria by the Islamic State group has made a televised plea asking his captors to free him.

Barbara Henning said "Please release him. We need him back home."

Alan Henning, a 47-year-old former taxi driver, was kidnapped in December after crossing from Turkey into Syria in an aid convoy.

In recent weeks, the militants have released online videos showing the beheading of two American journalists and a British aid worker, and threatened to kill Henning next.

Barbara Henning has previously released messages through Britain's Foreign Office appealing for the militants to get in touch with her family.

She said Tuesday the family had has been given hope by "the outcry across the world" over Alan Henning's imprisonment.