The wife of British hostage Alan Henning pleaded Saturday with ISIS to release him, describing her husband as a "peaceful, selfless man" who was only in Syria to help people in need.

"I cannot see how it could assist any state's cause to allow the world to see a man like Alan dying," Barbara Henning said, according to a message released by the UK Foreign Office. ISIS refers to itself as "the Islamic State."

Alan Henning, a taxi driver from near Manchester, England, was part of a team of volunteers that traveled to Syria in December to deliver food and water to people affected by the Middle Eastern country's devastating civil war.

He was abducted the day after Christmas by masked gunmen, according to other people in the aid convoy.

In a videotaped execution of British aid worker David Haines, made public last weekend, ISIS displayed Henning and threatened to kill him next.

The Sunni extremist group, which controls large areas of Iraq and Syria, has already beheaded three Western captives in recent weeks -- Haines, and the American journalists James Foley and Steven Sotloff.

The videos of the executions have pointed to U.S. airstrikes against ISIS forces in Iraq as the motivation. In Haines' case, the militant group described the killing as "a message to the allies of America."

Henning's wife said her husband, a father of two, was only trying to do good in Syria.

"Alan is a peaceful, selfless man who left his family and his job as a taxi driver in the UK to drive in a convoy all the way to Syria with his Muslim colleagues and friends to help those most in need," she said in the statement.

She expressed concern that his captors weren't answering her calls for his release.

"I have sent some really important messages but they have not been responded to," she said.

(CNN)