Foreign Minister Bob Carr says a major military defection and an assassination seem to be pre-conditions of movement towards peace in Syria.

Senator Carr says while there is nothing to suggest it is about to happen, the battle between president Bashar al-Assad's regime and opposition fighters has become more even.

He has told the ABC's Four Corners program it seems to be the pre-condition for movement towards peace.

"I think we'd know the conflict has evened up if there is a major defection from the Assad government, especially a defection that takes part of its armed forces with it," he said.

"This sounds brutal and callous, perhaps an assassination combined with a major defection, taking a large part of its military, is what is required to get one; a ceasefire and two; political negotiations.

"I know of no intelligence data - none has flowed across my desk - that suggests this is about to happen but it would seem to be a pre-condition of movement towards what Kofi Annan said was essential and that is a ceasefire and two negotiations between all sides towards what was laid out at the Geneva conference in June."

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Senator Carr says Mr Assad's military regime has not accommodated the desire for change among Syrians, which has resulted in the bloodshed.

"We've got nothing to do but trust the spirit of the Arab Spring," he said.

"We do know there is a body of opinion in the Arab world running strongly that says 'we do not want extremism, we want democracy denied to us for so long'."

Senator Carr says it is unclear to what extent Islamic extremists like Al Qaeda are involved in the conflict.

Tens of thousands of people have fled Syria since an uprising against Mr Assad's regime began more than 18 months ago.

Opposition activists estimate 30,000 people have been killed in the conflict which has developed into a full-scale civil war.

While opposition forces lack the strength to defeat the government forces outright, the military struggles to maintain control of many areas in the city - resulting in significant loss of life.