Australian Super Hornets have increased their sorties over Iraq in the past week to allow the US and other coalition forces to concentrate their air strikes around the Syrian city of Kobane.

Chief of Joint Operations Rear Admiral David Johnston told a briefing in Canberra the Australian jets had now flown 43 sorties since combat operations began.

Bombs had been dropped on at least two occasions, the latest of which resulted in the deaths of an unspecified number of Islamic State (IS) fighters.

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The targets have been Islamic State equipment facilities.

Rear Admiral Johnston confirmed a number of IS fighters had been killed in the missions, but refused to specify exactly how many.

He said the Australian strikes had had a significant impact on IS morale, undermining the group's notion of invulnerability.

The strikes had also destroyed a number of oil facilities and as such had had a significant impact on potential revenue streams for IS, he added.

Rear Admiral Johnston described the situation in Kobane as serious and said IS fighters had made significant advances in recent days.

"ISIL [Islamic State] is clearly very determined but they're suffering hundreds of lives lost", he said.

Kurdish forces are said to have hit back overnight but the outcome for Kobane remains uncertain.

Last week Turkish and US officials said IS was on the verge of taking Kobane from its heavily outgunned Kurdish defenders, after seizing strategic points deep inside the town.

IS's Kobane offensive is one of several it has conducted after a series of lightning advances since June, which have sent shockwaves through the region and sparked alarm in Western capitals.

Turkey has refused to bow to pressure to aid Kobane, either by ordering in Turkish tanks and troops that line the border, or permitting weapons and ammunition to reach the town.

Officials were also wary of arming Kobane's Kurdish defenders, who have strong links with the militant Kurdistan Workers' Party (PKK).

Turkish officials are increasingly frustrated with criticism of their actions towards Kobane, and have said they have carried the humanitarian burden from the fighting, which has seen 200,000 people cross the border from the Kobane area.

Two hundred Australian special forces are still waiting at a base in the United Arab Emirates to be deployed to Iraq.

No move will be made until the legal framework can be put in place for their deployment.

The Australian Government is still waiting for the Iraqi government to appoint a defence minister, but Rear Admiral Johnston said he thought the legalities would be sorted out within days.

He said he was "confident we will get in and confident we will make a contribution" once the deployment was approved.