Australian troops must face the Islamic State, which is a “cancer” whose “medieval” ways have led to another beheading, says Immigration Minister Scott Morrison.

“[Australian forces] are there to degrade and destruct and do whatever is necessary to ensure that this horrible death cult and cancer cannot continue to have its way,” Morrison said outside Lakemba Mosque in western Sydney.

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In a video showing his execution, the IS jihadist group claimed responsibility for the murder of British aid volunteer Alan Henning.

“That is just another horrific and brutal and medieval example of what the Australian defence forces are going there to combat,” the minister said.

The group also threatened American hostage Peter Kassig, another aid volunteer captured in Syria.

Mr Morrison said the jihadist group was not representative of Muslims.

“That has nothing to do with the true faith you see on display here today,” he said outside the mosque.

Opposition Leader Bill Shorten said the latest murder only strengthened people’s resolve to stop the group.

“This dreadful murder doesn’t make people shy away,” he told reporters at Belmore in Sydney.

“I just think it strengthens the resolve of people of good conscience everywhere to put a stop to this crazy violence.”

Mr Shorten said he didn’t know how long the conflict would last, but troops wouldn’t be in Iraq “forever and ever”.

Military action was based on humanitarian support and requests for help by the Iraqi government, he said.