Prime Minister Tony Abbott has warned Australian jihadists in Syria that they "may well feel the force of our arms" as he approved RAAF bombing raids deep into the Islamic State group's heartland. 
Mr Abbott also refused to rule out putting combat boots on the ground in future as he confirmed on Wednesday that cabinet had given the go-ahead for expanded air strikes from Iraq into Syria, which are set to start within a week.
However, he said he has no plans to broaden Australia's military involvement to target the brutal Syrian regime in the capital Damascus.
Mr Abbott said anyone fighting with the Islamic State was a "potential target" including the estimated 120 Australians with the group, most of them believed to be in Syria.
"If people are fighting for Daesh [IS], if they are working for the death cult and they come within the rules of engagement, well, obviously, they may well feel the force of our arms," Mr Abbott said.
Labor backed the expansion, with Opposition Leader Bill Shorten telling Parliament that this was a just cause against an "evil" enemy.
But he demanded assurances that Australian strikes would be restricted to stopping cross-border attacks by the Islamic State into Iraq.
The legal justification being cited by the government is one of "collective self-defence" of Iraq.
However, Defence Minister Kevin Andrews revealed in an interview on Sky News that Australia's operations could stretch as far as the Islamic State de facto capital of al-Raqqa, about 200 kilometres from the Iraq border.
"The region could extend as far as al-Raqqa but where we're not going is over into the west of Syria. We're not going into the areas of Damascus or Aleppo where the conflict between the Assad and anti-Assad forces is going on," he said.
The refugee crisis facing the Middle East and Europe is being driven not just by Islamic State but by the broader Syrian civil war, not least atrocities carried out against civilians by dictator Bashar al-Assad.
Mr Abbott stressed that RAAF strikes would be confined to Islamic State targets, though he noted the Assad regime was "evil" and Australia would like it to fall.
"We have no legal basis, at this point in time, for wider strikes in Syria and we don't intend to make wider strikes in Syria," he said.
Seeking to distinguish the mission from the 2003 invasion of Iraq, Mr Abbott said that "this is not an attempt to build a shining city on a hill".
"That's been tried and it didn't magnificently succeed," he said.
The Chief of the Defence Force, Mark Binskin, said Defence hoped to start operations over Syria "within the week".
The risk to RAAF pilots of flying over Syria compared with Iraq was not "a marked increase", he said.
Coalition forces were aware of what the Syrian military was doing and ensured they did not cross paths.