The prospect of Australian participation in a war against Islamic State fighters in Iraq is edging closer with both Tony Abbott and Bill Shorten in lockstep yesterday branding the militants respectively "a death cult" and "an enemy of humanity".

In powerful statements to Parliament, the two leaders took a common position in declaring that Australia and its allies and partners could not stand by while innocent people were slaughtered.

Building the moral case for intervention, Mr Abbott said that Australians "in good conscience … cannot leave the Iraqi people to face this horror, this pure evil alone, or ask others to do so in the name of human decency what we won't do ourselves".