The Prime Minister also pointedly declined to rule out expanding Australian air strikes into Syria during his Tuesday morning announcement that cabinet had signed off on the deployment, under which about 330 Australian troops will train the Iraqi military at Taji base north of Baghdad.

"It's not a combat mission, but Iraq is a dangerous place … and I can't tell you that this is risk-free," Mr Abbott said.

The Australian troops, mostly drawn from the army's Brisbane-based 7th Brigade, will work alongside about 100 New Zealand soldiers. They will be fully deployed and operational by the middle of May, Mr Abbott said.

The mission was set for two years with a formal review after 12 months.

Mr Abbott said any decision on broadening Australian involvement beyond Iraq into neighbouring Syria was yet to be made.

"We've made no decision along those lines and we have no plans to extend our air campaign at this stage," Mr Abbott said.

But he added that he was "conscious" of the decision by Canada – which has deployed a very similar force to that of Australia – to expand its air strikes into Syria and said Australian refuellers and radar planes were already helping with other countries' strikes inside Syria.

The Australian training deployment meanwhile is likely to have to wrestle with one of the emerging complexities of the Iraq campaign to beat back the Islamic State terror group: the role of irregular Shiite militias in Iraq.

These militias have been doing some of the heaviest fighting and achieved some of the most significant gains against Islamic State on the ground. But they are backed by Iran – which is increasing the Shiite regional giant's influence in Iraq – and have been accused of atrocities themselves.

Western military planners are also concerned that the role of Shiite militias may drive more Sunnis into the arms of the Islamic State, also known as ISIL or Daesh, given the deep sectarian mistrust in the country.

These militias reportedly have a heavy presence around Taji and even may have access to the base where the Australians will be working. The Wall Street Journal reported at the weekend that some of the Iraqi soldiers being trained by American troops at Taji base are "moonlighting" with irregular militias on their days off.

Also last week, the Iraqi cabinet decided to bring some of the militias under the control of the Interior Minister, making them semi-official.

The Chief of the Defence Force, Air Chief Marshal Mark Binskin, praised this move as an effort to bring the militias under greater control.

"That was a move from the Iraqi government to understand that they needed to bring all forces under some structured command and control. Any time they do that, that's a good move," he said.

Mr Abbott added: "The stronger the Iraqi regular army is, the less likely it is that Shiite militia will play a continuing role the ultimate retaking of the country. So by strengthening the Iraqi Army, we are giving the Iraqi government a whole lot of options that it may not currently have."

Air Chief Marshal Binskin said the Australian forces had been exercising with their New Zealand counterparts to prepare for the training mission.

Defence Minister Kevin Andrews said the decision to deploy further Australian troops had not been "taken lightly" but was in the national interest because of the threat Islamic State posed to the Middle East and to Australia.