The veteran of the last Iraq war said it was crucial that the lessons of past interventions were observed "because we have experience in previous conflicts, we know it's the thin end of the wedge". Departure: Over 80 troops checked through Sydney Airport's commercial terminal en route to Iraq. Credit:Diimex While a contingent of SAS commandos departed for the Middle East on Monday, Fairfax Media understands several SAS commandos have been in the region on standby for weeks. Mr Abbott's comments came as US airstrikes on Islamic State (IS) positions south-west of Baghdad and around Sinjar were launched on Monday. Mr Abbott said the fact that the legitimate government of Iraq had invited Australia to assist in defeating an insurgent force, made Australia's participation in the air and ground war legal.

"I'm not ruling out some action in Syria but it is not part of the government's current intentions because, as I've said quite frequently over the last few days, the legalities of operations in Syria are quite different from the legalities of operations in Iraq," he said. But a possible future expansion of Australia's role - often dubbed mission creep - either by using Special Forces to attack IS Federal Labor MP Melissa Parke has already questioned the wisdom of the campaign and plans a further statement to the Parliament. Opposition leader Bill Shorten said Labor was united in support for the government's approach but he qualified that on Tuesday by warning his party would not support Australian units fighting in Iraq. "We don't support sending formed-up combat units to fight on the ground directly against IS, but if the Iraqi national government, in pursuit of protecting innocent civilians, through the United States, is requesting some Australian assistance, I think that's appropriate".

The government has expressly ruled out any "independent" combat role for Australian forces, but Mr Shorten's statement appears to have placed an outer-limit on Labor's support and therefore narrowed the range of future options open to the Abbott government as the conflict develops. Speaking from the Northern Territory where he has based himself for most of the week, Mr Abbott revealed the cost of Australia's open-ended commitment to the anti-IS fight in Iraq, putting it at around $250 million per six month rotation. Branding the growing coalition of nations backing action in Iraq as "the coalition of the concerned", Mr Abbott admitted Australia's forces would be engaged in "forceful" combat missions against IS forces. Mr Abbott said there was no risk-free way to carry out combat operations in Iraq. "I have said from the beginning that any combat operations inside Iraq would be hazardous – highly hazardous," he said. The US airstrikes mark the beginning of a new and aggressive assault on IS.

Some 160 airstrikes have been mounted by the US in the past month but these had ben restricted to defending stranded local populations of religious minorities. The raids on Monday were targeted directly at IS positions for the express purpose of inflicting maximum damage to the terrorist forces. Mr Abbott said there were real dangers involved in the mission, even as he refused to describe Australia as being at war. "What I'm talking about is Australia's readiness to engage in combat operations inside Iraq," he said. "Yes, we are prepared to be military advisers to the Iraqi security forces and to the Peshmerga but this is a fight, there's no doubt about that, this is a fight, and we are determined to act forcefully with the full support, co-operation of the Iraqi government, to be as helpful as we possibly can."

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