Australian police have obtained arrest warrants for two Australians who are fighting with the Islamic State group in Iraq and Syria after one posted photographs of the other posing with severed heads of Syrian soldiers.

Australian Federal Police said in a statement on Tuesday that they obtained arrest warrants for Khaled Sharrouf and Mohamed Elomar for "terrorism-related activity".

The former Sydney residents will be arrested if they return to Australia, the statement said.

Photographs posted last week on a Twitter account linked to Sharrouf showed Elomar smiling and holding the severed heads of two Syrian soldiers.

Last month, The Australian newspaper published a photograph of Sharrouf posing among the bodies of massacred Iraqis.

The pair travelled late last year to Syria and then Iraq to join the fighters.

The Australian government said last month that 150 Australians have fought with fighters in Syria and Iraq, raising fears of a threat to Australia if the fighters return home.

Sharrouf was among nine Muslim men accused in 2007 of stockpiling bomb-making chemicals and plotting terrorist attacks in Australia's largest cities, Sydney and Melbourne.

He pleaded guilty to terrorism offences and was sentenced in 2009 to four years in prison.

Australia prohibits suspected terrorists from leaving the country, but Sharrouf used his brother's passport to leave Australia, the government says.