Sydney: Former US military commander David Petraeus said Wednesday fighters from al Qaeda`s Syrian affiliate could be used to take on the Islamic State group as he warned that his nation`s hesitation to enforce "red lines" in Syria had damaged US credibility.
The decorated four-star general said a controversial move to harness fighters from a group linked to al Qaeda -- which was responsible for the September 11, 2001 attacks -- was "an option that has some prospect for achievement".
Petraeus, who was feted for changing the course of the Iraq war in 2007, said the focus was not on cooperating with the leaders of al Qaeda affiliate Al-Nusra Front but with its fighters, using similar strategies from the previous conflict.
"There are elements... who for reasons of opportunism or convenience ended up fighting under Jabhat al-Nusra as they realised that the moderate opposition was not yet sufficiently resourced," he told the Lowy Institute think-tank in Sydney.
"I don`t know whether it means there will be... the kinds of tens of thousands that we were able to strip away from the Sunni insurgents in al Qaeda in Iraq which was so instrumental ultimately in not just defeating it, but destroying it by the end of the surge."
Petraeus` comments followed a statement he issued to CNN Tuesday about using al Qaeda-linked jihadists, with the proposed move reflecting the complex military campaign the US-led coalition is waging against IS in Syria.
In a speech calling for active US engagement in both the Middle East and Asia-Pacific regions, Petraeus said there were lessons from the failure to act when Syrian leader Bashar al-Assad breached the US government`s self-declared "red lines".
"(The) hesitation... caused tremors not only in the Middle East, but also among some of our friends in the Western Pacific, who also have a strong stake in America upholding its `red lines`," the former CIA director said.
"There is no clearer, more cautionary tale about the indivisible nature of American credibility in Asia and in the Middle East, no more dramatic illustration that how the way we act -- or don`t act -- in one theatre can have an impact in the other and far beyond."
Australia is part of the US-led fight against IS in Iraq through airstrikes and special forces soldiers, and is considering an American request to extend its air campaign into Syria.
"I think that taking such an action together with other coalition members will do damage to ISIS," Petraeus said of Australia`s possible expansion of its involvement in the conflict.
Petraeus, who led the US wars in Iraq and Afghanistan, fell from grace earlier this year when he was given two years` probation and fined US$100,000 for providing classified information to his mistress and biographer Paula Broadwell.