Tony Abbott says humanitarian intervention limited to Iraq

As the government indicated that evidence of massacres in northern Iraq by Islamic State militants was continuing, Mr Abbott stuck by his position that Australia would consider requests by Washington for military assistance if the humanitarian objectives were clear and the risk to troops proportionate.

But asked whether the government might broaden the doctrine of humanitarian interventions, Mr Abbott said he would be reluctant.

"I'm very reluctant to embrace doctrine because doctrine can easily become doctrinaire behaviour and I don't believe that any Australian government should ever find itself caught up in doctrinaire behaviour," he said.

"But it is important to do what we can to help, where there is something useful that we can do and that is what we are talking to the United States and to our other allies and partners about."

Mr Abbott repeated that IS represented "pure evil" that needed to be "dealt with".

"We have seen what they can do. We have seen the beheadings, the crucifixions, the mass executions," he said.

A well-informed source in Washington said there was a view within the Obama administration that IS must be attacked militarily. But the White House also believes an expanded assault from the air would be ineffectual unless it was made with the support of Sunni tribes within Iraq, and their supporters among the Gulf states and Saudi Arabia.

Until such a coalition can be brought together that would rob the IS of some of its Sunni support – a process that could take weeks – the US is likely to continue with its campaign of limited air strikes to blunt the militants' advances.

Defence Minister David Johnston, speaking at Richmond RAAF Base where he visited the crew from the 37 Squadron who took part in a recent humanitarian air drop over Iraq, said there was evidence the village of Kojo in northern Iraq had been the site of a major massacre.