Prime Minister Tony Abbott has stepped up his rhetoric to prepare Australians for a possible intervention in chaos-torn Iraq, saying "no human being" should ignore the "slaughter of innocent people".

Amid continuing reports of massacres in the country's north, Mr Abbott has painted a grim picture of the persistent threat of genocide by the brutal Islamic State, laying the case for intervention.

While sticking to a previous statement that no official request for help has yet come from the United States, Mr Abbott indicated Australia would be prepared to contribute militarily if the mission purpose had clear humanitarian goals and the risk to military personnel was acceptable.

"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," he said in Parliament.