"Australia has not been officially asked for military assistance," Abbott said.
"Should we be asked, we would want to look at any request in the light of achievable objectives, a clear role for Australian forces, a full risk assessment and an overall humanitarian objective."
Any decision to send troops would be made in consultation with Cabinet and the opposition, he said.
News reports say the United States is considering asking Britain and Australia to support air strikes in northern Iraq.
The New York Times said US officials believed "Britain and Australia would be willing to join the United States in an air campaign".
President Barack Obama is ready to authorise air raids and aid drops around the town of Amerli, home of Iraq's Turkmen minority, where 12,000 people have been under siege by Isis extremists for two months.
A spokesman for the British Embassy in Washington said: "There's been no request for us to deliver air strikes and this is not something under discussion at the moment."
Obama is also contemplating airstrikes in Syria and faces a familiar question: Should Congress have a say in his decision?
Obama was proposing strikes last year when he abruptly announced that he first wanted approval from Congress. But legislators balked at his request for a vote and the operation was eventually scrapped.
This time, the White House is suggesting it may not be necessary to get approval from Congress.
Officials say there is a difference between last year's effort to attack Syria's government in retaliation for chemical weapons use and the bombing campaign against Isis now being considered.
"What we're talking about now is confronting a terrorist group that has sought safe haven in Syria," White House spokesman Josh Earnest said. "This is a group that poses a threat to Americans in the region and could, down the line, pose a broader threat to American interests and our allies around the globe."
In Syria's Aleppo, devastated by two years of fighting, rebels and activists are eager for US strikes against jihadists they say have stolen their anti-government uprising. Isis's campaign of extreme violence and abuses against both civilians and rival opposition groups has prompted a backlash across rebel-held Syria.
"They have ravaged the country, oppressed the people, make no distinction between combatants and civilians, and slaughtered with knives," said Abu Al-Muqdad, a fighter in Aleppo with the Islamic Front, a rebel coalition.
- Telegraph Group Ltd, AAP, AFP, AP
