APN Newsdesk and INM

By Emma McBryde and The Independent

Prime Minister Tony Abbott has ignored warnings Australia involvement in the attack on the Islamic State could incite further Muslim radicals nationwide by committing 600 troops to the US-led operation.

But Mr Abbott said the troops, made up of 400 airforce and 200 military, would not be in combat when he made the announcement while visiting troops in Darwin.

Mr Abbott described ISIS as a "death cult", speaking of beheadings and crucifixions committed by the group.

His announcement came not long after ISIS released another video showing a third beheading of a Westerner, British aid worker David Haines.

"We are not deploying combat troops but contributing to international efforts to prevent the humanitarian crisis from deepening," he said.

Mr Abbott said it could be a lengthy operation.

The decision came after the US made a formal request for troops.

The troops and a special operations task group who will act as military advisers to Iraqi and other security forces will be sent to the United Arab Emirates.

"The conflict has reached out to Australia, with at least 60 Australians fighting with ISIL and other terrorist groups and another 100 or so supporting these extremists," Mr Abbott said.

Greens leader Christine Milne has condemned the government's decision to follow the US in sending troops.

"It's time Australian's recognised we need to have our own independent foreign policy," she said.

But Immigration Minister Scott Morrison told television presenter Andrew Bolt the government needed to ensure Australia was safe.

"We should never be intimidated by this," Mr Morrison said.

"There is no excuse for terrorism, there is no excuse for extremism, and there's certainly no justification for it, and we'll act in our national interest."

But Tom Switzer from the United States Studies Centre of the University of Sydney told the ABC the majority of Australians are backing involvement in this operation.

"This is a broadly popular war, although it's not called a war," he said.

Mr Switzer said 63% of people surveyed by Newspoll had backed involvement.

Philippe Sands QC, professor of international law at University College London, has warned that the Prime Minister would struggle to justify UK support for US-led air strikes on Islamist extremists in Syria.

Mr Sands said not only was there no authorisation from the United Nations Security Council, there is no apparent evidence of self-defence and little precedent for launching any attack on "humanitarian grounds".

This article was originally published at APN Newsdesk and INM