The prime minister's office has denied reports an Australian C-130 Hercules aircraft was shot at while delivering humanitarian aid to besieged Iraqis.

News Corp Australia reports the RAAF transport was attacked by Islamic State extremists as it swooped to drop aid to the the town of Amerli in northern Iraq.

But a spokesman for Prime Minister Tony Abbott said it wasn't fired on.

"Our plane did not report being fired on," he told AAP on Tuesday.

News Corp reported that the C-130 was delivering food, water and hygiene packs under the cover of darkness when the attack took place

The reports claimed a US military plane acting as cover fired upon the extremists, neutralising the threat.

The RAAF is also taking part in an international airlift of military equipment to Kurdish forces battling IS fighters around Erbil.