Up to 40 Australian women have either joined terror groups abroad or are supporting them from home, the Abbott government has said as it prepares to expand the nation's contribution to the fight against the Islamic State.

Foreign Minister Julie Bishop told federal Parliament on Wednesday that more young people and women were travelling to Syria and Iraq to join groups such as the Islamic State.

"Yet more women are either joining their foreign fighter husbands or are apparently seeking to find partners — the so called jihadi brides — or are otherwise providing support for terrorist organisations," she said.

As Fairfax Media reported on Saturday, the Abbott government is poised to announce it will send between 200 and 300 Australian Defence Force troops to train the Iraqis on bases in conjunction with New Zealand forces.

The national security committee of Cabinet met on Tuesday night and is understood to have discussed the deployment. Prime Minister Tony Abbott said on Wednesday he would have more to say on the issue soon.

The Chief of the Defence Force Mark Binskin confirmed to a Senate estimates hearing on Wednesday he had worked with his New Zealand counterpart on a further training mission to Iraq but said "no final decision" had been made by the Abbott government.

Fairfax Media understands that the new training force will remain "behind the wire" on bases. Senior sources have told Fairfax Media that the new training forces are expected to start work in the war-torn country by the middle of this year.

But the 200 commandos currently on the ground are expected to start drawing down over the second half of 2015, meaning that by the end of the year, the total number of Australians on the ground will only be slightly higher than it is now.

Ms Bishop said it "defies logic" that women would join groups like the Islamic State.

"We know the attitude of Daesh towards women," she said, using the Arabic acronym for the group. "If the killings and executions aren't enough, Daesh has published instructions on the treatment of sexual slaves which includes raping and beating women. Even children are not immune with instructions encouraging sexual assault on girls who've not yet reached puberty."

Secretary of the Defence Department Dennis Richardson warned in the Senate hearing that Islamic State was a formidable fighting force commanded by experienced leaders, and said it would likely be three years before the Iraqi security forces were able to provide stability in the country.

"It is not a rabble of immature foreign fighters that is running around on the back of utes," he said.

"It is led by experienced former Iraqi generals and others with substantial military experience. As brutal and as nasty and terrible as ... they are, as an enemy, you shouldn't underestimate their capability."

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