Australia on Tuesday accused Islamic militants of using foreign fighters as "cannon fodder" and "propaganda tools" as it revealed 20 nationals have now been killed in Syria and Iraq.

More than 70 Australians are currently fighting in the two nations, the government has said, with several more deaths reported as coalition fighter planes pound Islamic State group positions.

"The government is aware of around 20 Australians who have died in the conflict in Syria and Iraq," Attorney General George Brandis told The Australian newspaper.

"This number has risen in recent weeks, with several Australians understood to have died in fighting against government forces, including in Kobane."

The Australian government had previously confirmed 15 deaths, with the tally climbing higher as fighting rages around the strategic Syrian town of Kobane.

The deaths have given rise to fresh warnings that foreigners are being exploited by Islamic State for what has become a public relations campaign aimed at driving recruitment.

Brandis accused the group of duping Western recruits into thinking they were "an important part" of a religious crusade when in fact they were bit players in a propaganda war.

"They are simply using them as frontline cannon fodder, suicide bombers and propaganda tools," he said.

"Australian youths, and many young men and women from Western countries, are being lured by the falsehood of a noble battle against an oppressive enemy.

"In reality, they are merely taking part in acts of thoughtless violence, in many cases against innocent civilians, on behalf of ISIL, which is intent on recklessly enslaving, raping and murdering those with a contrary view to their own."

Canberra recently passed a law criminalising travel to terror hotspots without good reason, fearful that nationals will pose a risk when they return radicalised.

Under new laws, anyone who heads to nominated areas will face up to 10 years in jail.

Many countries are facing similar issues with new European Union foreign policy chief Federica Mogherini saying Monday she hoped increased intelligence-sharing would help stop the flow of foreign fighters.