After meeting world leaders at the United Nations in New York, Mr Abbott was flying home to brief cabinet on Australia's participation in joint military action.

In doing so, he confirmed what has been an open secret in defence circles from the moment Australia signalled its support for a US-led assault on Islamic State insurgents operating in Iraq and back and forth to Syria.

That is, that the final commitment to go to war was all but inevitable.

"We didn't send them there for merely an exercise," Mr Abbott said of Australia's deployment to the United Arab Emirates of 600 personnel, eight FA-18 Super Hornets, and other early-warning and refuelling aircraft.

"We sent them there in readiness to deploy them, but obviously, it's important to do so as part of a coalition.

"That coalition clearly is assembling and the government will be making further decisions in coming days."

Mr Abbott was one of some 130 world leaders in New York this week for the General Assembly of the UN, and for a special UN Security Council meeting chaired by US President Barack Obama, specifically called to discuss the terrorist threat arising from the IS campaign in Iraq and Syria.

While most leaders - Mr Abbott being an exception - also were in New York to attend global climate change talks promoted by the UN Secretary-General Ban Ki-moon, and Mr Obama, the week was largely dominated by the gathering war in Iraq and Syria, especially as the US aerial bombing of targets in Syria commenced on Tuesday aimed at taking out IS leaders and the force's training and communications facilities.

Another foreigner recently kidnapped by radical Algerian Islamist group Jund al-Khilafa was killed on video for propaganda purposes. The group had been part of al-Qaeda and has roots in the Algerian Islamist movement which took part in the civil war in that country in the 1990s.

Herve Gourdel was killed by IS-linked terrorists in recrimination for French airstrikes on IS positions.

He was beheaded this week in a gruesome video killing, further stoking the pro-war sentiment among international leaders.

The coalition of countries pledging support for the US-led action to disrupt, and ultimately destroy Islamic State is said to exceed 40 and could be as many as 50.

Among those are key Sunni Arab states previously close to Syria and strongly disinclined to associate with US interference in the Middle-East.

There is now a palpable sense among world leaders that the bombing campaigns will step up along with ground forces supplied mainly by Iraq and the Kurdish Peshmerga.

Mr Obama met Iraqi Prime Minister Haider al-Abadi after which the Iraqi claimed his intelligence agencies had identified a plot to bomb US and French subway stations.

The US subsequently denied having any knowledge or intelligence about the plot.

Australia's forces on the ground in the theatre of war will be restricted to advisory and training roles but will be armed and able to shoot back at aggressors.

Mr Abbott again ruled out deploying actual ground combat troops but left open the possibility of extending the mission into Syria despite legal difficulties should that be required.

"I certainly don't rule it out. Morally, there's little difference between ISIL – this death cult – on one side of the border to the other because it's a border that ISIL doesn't recognise," he told the ABC.

"But legally – and the Australian government must be conscious of these things because we are a law-abiding country – legally, there's a world of difference between operating inside in Iraq in support of and at the request of the Iraqi government, and operating in Syria which is largely ungoverned space with a regime that Australia doesn't actually recognise."