Australia's cabinet has authorised military air strikes on the Islamic State of Iraq and the Levant (ISIL) group on Iraqi territory and the deployment of special forces troops to combat the fighters.

Prime Minister Tony Abbott said the deployment to Iraq "could be quite lengthy. Certainly, months rather than weeks."

He said the decision to intervene came at the request of the Iraqi government and that it was in Australia's national interest.

"Yes, it is a combat deployment, but it is an essentially humanitarian mission to protect the people of Iraq and ultimately the people of Australia from the murderous rage of the ISIL death cult," Abbott said.

"ISIL must be disrupted and degraded at home and abroad, so it is absolutely in Australia's national interests that this mission go ahead," he said.

Australia recently heightened its security alert, citing threats attacks by ISIL sympathisers on its soil.

ISIL has seized large swathes of territory in Iraq and neighbouring Syria. The UN has accused the group of carrying out a "staggering array" of human rights abuses that may amount to war crimes, attacking civilians and committing targeted executions, abductions and rape.

On Thursday, Turkey's parliament authorised the government to carry out military operations in Iraq and Syria to fight ISIL and other armed groups. The vote also allows foreign soldiers to be stationed in Turkey and to use its military bases for the same purposes.

'ISIL in retreat'

The announcement that Australia will participate in air strikes came days after its military jets took part in support missions over Iraq with the US-led international coalition.

"It could take quite some time, but we will know that we are succeeding, when ISIL are in retreat, not in advance. We will know that we are succeeding when the Iraqi government is restoring a modicum of control over its own cities and towns," Abbott said.

The announcement of an Australian combat role on Friday has been widely anticipated since the Super Hornets were pre-deployed to the United Arab Emirates more than two weeks ago in response to a formal request from the United States for specific contributions to the international coalition.

Defence Force Chief Air Chief Marshal Mark Binskin said the air strikes would start "over the coming days," but would not be more specific.

Two unarmed Australian air force planes - an E-7A Wedgetail surveillance and communications jet and a KC-30A refuelling plane - joined operations over Iraq from the al-Minhad Air Base outside Dubai for the first time on Wednesday in support roles.

The government says the number of Super Hornets could soon be increased to eight.

The Australian deployment also includes a 200-strong ground force, including special forces, to advise security forces inside Iraq, plus 400 air force personnel.

The special forces will also deploy to Iraq to "advise and assist Iraqi security forces" once the appropriate legal arrangements were in place with the Iraqi government, Abbott said.

Abbott has restricted combat operations to Iraq and has ruled out Australian troops fighting on the ground.

Australia is among dozens of countries from Europe, Middle East and including Canada that have signed up to the US-led coalition fighting ISIIL in Iraq and Syria. Contributions vary and include military assistance and humanitarian aid as well as carrying out air strikes.