Attorney-General George Brandis says he is "appalled" by the latest beheading of a foreign national by the Islamic State jihadist group, saying the third-such execution in recent weeks demonstrates why the group is a "fundamental threat to the Western world."

Senator Brandis said the newest "barbarity" underlines the reason why Australia is "engaged" with international efforts to confront the terrorist organisation in the Middle East, along with the United States.

A video purportedly showing threats being made to a man Islamic State (IS) named as David Haines. Credit:AP

"I'm appalled by this," he told the ABC's Insiders program.

"It just serves to demonstrate, not that it's really necessary for there to be more evidence, how barbaric and evil these people are."