Australia PM Says 'Extreme Force' Justified against IS

Prime Minister Tony Abbott on Tuesday said "extreme force" was justified in battling Islamic State militants as he played down reports that an Australian plane delivering humanitarian aid in Iraq came under fire.

Australia will "in coming days" join ally the United States in an international effort to transport weapons to Kurdish forces fighting IS extremists in northern Iraq.

It has also been conducting humanitarian air drops to the besieged town of Amerli.

While Abbott has insisted Canberra will not be sending combat troops to the conflict, he has stepped up his rhetoric against the jihadist group, calling it a "death cult" carrying out ethnic cleansing.

On Tuesday he compared them to the Nazis and communists.

"The difficulty here is that these people do exalt in death; they absolutely revel in killing," he told Sydney radio station 2GB.

"We've seen in the century just gone, the most unspeakable things happen, but the atrocities that were committed by the Nazis, by the communists and others, they were ashamed of them, they tried to cover them up.

"This mob, by contrast, as soon as they've done something gruesome and ghastly and unspeakable, they're advertising it on the Internet for all to see which makes them, in my mind, nothing but a death cult.

"That's why I think it's quite proper to respond with extreme force against people like this."

IS has prompted widespread concern as it advances in Syria and Iraq, killing hundreds of people, including in gruesome beheadings and mass executions.

Abbott's comments came as a senior U.N. rights official said IS had carried out "acts of inhumanity on an unimaginable scale".

Australia is gearing up to fly a C-130 aircraft to the Iraqi capital Baghdad for customs clearance "in coming days", before heading to Kurdish-controlled Erbil. The plane will then reportedly land to hand over weaponry, which will include mortars and rocket-propelled grenades.

The dangers faced by Australian and allied forces was highlighted Tuesday with a report that a C-130 Hercules came under machine-gun fire as it dropped aid to Amerli.

Abbott said he had not been fully briefed on what might have happened.

"I've seen the report in the paper and yes, they were flying into an active combat zone, so there may well have been fire in the area, but I'm not advised that they came under direct fire themselves," he said.

"Obviously, flying into a war zone, combat zones, air drops, even humanitarian air drops into combat zones are full of risk, but the risks are reasonable given the importance of the missions they're flying."