American journalist Naomi Wolf has questioned whether videos of executions carried out by Islamic State terrorists in Iraq are genuine.

The Jewish writer, a former political consultant and best-selling feminist author, posted a message on Facebook apparently suggesting aid organisations had not reported any workers as having been taken hostage.

Referring to the beheading videos on the internet, Ms Wolf said it would take “five people to stage an event like this”. She questioned why the media did not investigate the validity of the films more carefully.

She said calling Isis “evil” was “not language of a news analysis”.

Ms Wolf later backtracked, claiming a New York Times reporter had told her a news blackout had been placed on reporting of a series of kidnappings in the region in the past two years.

She added: “It is a terrible thing, a verified video of an assassination, of course. That should go without saying.

“But many stories the New York Times and other major outlets have run based on government assurances – including the weapons of mass destruction story – seemed very solid at the time and one would have sounded disrespectful at the time to request confirmation of the reporting.

“But confirming important news stories is really what reporters are supposed to do. And citizens should be trained to do it too if democracy is to be strong and journalism as well.”

Ms Wolf also appeared to suggest American troops were being used to bring the ebola virus to the United States from Africa.

A video showing the killing of British aid worker Alan Henning was posted online on Friday.