SYDNEY - Australian aircraft will join the US-led coalition in air strikes against Islamic State insurgents in Iraq in an initial support role, Prime Minister Tony Abbott said on Wednesday, ahead of a final decision to undertake bombing missions.The United States has been bombing Islamic State and other groups in Syria for a week with the help of Arab allies, and hitting targets in neighboring Iraq since August. European countries have joined the campaign in Iraq but not in Syria.Last month, Abbott sent 10 aircraft and some 600 personnel to the United Arab Emirates in preparation for joining the coalition and has since said Australian involvement in air strikes was likely to combat the "murderous death cult.""We have not yet made a final decision to commit our forces to combat but Australian aircraft from today will start flying over Iraq in support of allied operations," Abbott told parliament. "Australian air strikes await final clearances from the Iraqi Government and a further decision by our own."Australia is on high alert for attacks by radicalized Muslims or by home-grown militants returning from fighting in the Middle East, having raised its threat level to high and undertaken a series of high-profile raids in major cities.Officials believe up to 160 Australians have either been involved in fighting in the Middle East or actively supporting it. At least 20 are believed to have returned to Australia and pose a security risk.One man was charged on Tuesday with funding a terrorist organization, while another was arrested last month after police said they thwarted a plot to behead a random member of the public.The Australian contingent in the UAE is made up of eight Super Hornet fighter jets, an early warning and control aircraft, an aerial refueling aircraft, along with 400 air force personnel and 200 special force soldiers.