Greens Leader Christine Milne has called on Australians to stand together against terrorism threats on home soil, saying unity, not war, will deliver lasting peace.

"The best way to keep Australians safe is to bring them together, not blindly follow the US into an unwinnable war in the Middle East," said Senator Milne.

"Are we going to another war in the Middle East because the terror alert has been raised, or the other way around?

Australian Greens Leader Christine Milne says Tony Abbott should level with the men and women of Australia's Defence Force when he farewells them tomorrow on an open-ended mission to Iraq.

"When you ask young men and women to put their lives on the line, you should be honest enough to tell them that you're committing them to war," said Senator Milne.

"This has been mission creep from the start. Australia is getting itself into an open-ended war.

The Australian Greens accept the advice of ASIO on threats to Australia but say we cannot ignore the impact of military engagement in Iraq and the Middle East in increasing the risk at home. Back in 2004, Federal Police Commissioner Mick Keelty said Australia was at increased risk because of our involvement in the Iraq war, and Greens Leader Christine Milne says the same applies now.

"We cannot bring Australians together and combat extremism at home by blindly following the USA into yet another Iraq war," said Senator Milne.

Greens Leader Christine Milne says Australia is witnessing mission creep in action, as the Foreign Minister says 'no boots on the ground,' but commits to joining an expanded military engagement in Iraq as soon as a formal request is made.

"Julie Bishop has written a blank cheque, telling the US it only needs to say the word and Australia will join in. But join in what?

"How long will military engagement in Iraq go on? What is the objective? Do we have any hope of achieving it?

As the extent of Australia's military involvement in Iraq remains unclear, Greens Leader Christine Milne explains why Australia should join many other democracies in giving the national parliament the final say on whether we go to war.

As the situation in Iraq deteriorates, Australian Greens Leader Christine Milne wants to give Parliament the authority to debate and vote on any military deployments, and is calling for Labor's support.

"Unlike many other democratic countries, Australia's military can be deployed overseas without any discussion or decision in the Parliament. This must change," said Senator Milne.

With reports coming out of the United States of possible Australian military involvement in Iraq and Syria, Greens Leader Christine Milne says it is essential that any decision to deploy our military is brought to the parliament.

"It is essential that PM Abbott commits immediately to bring any debate about the deployment of Australian military to the parliament for debate," Greens Leader Christine Milne said.