Deputy Liberal leader Julie Bishop says she has yet to be convinced the Syrian regime has used banned chemical weapons.
The US Congress will this week debate the issue of a possible strike on Syria - and US President Barack Obama will address his nation on the case for military intervention.
Both Kevin Rudd and Tony Abbott were briefed on the crisis and possible responses from Australia and its allies during the federal election campaign.
Mr Rudd said the evidence the Syrian regime was behind the deadly attack was "overwhelming".
But Ms Bishop, who is poised to become Australia's next foreign minister, says she has not received the same briefings.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
She has, however, discussed the issue with British Foreign Secretary William Hague and will speak to him again this week.
"I've not yet been briefed on the evidence that the United States says it has to prove that chemical weapons were used," she told Sky News on Sunday.
"I've not had that briefing."
