Two men identifying themselves as Australian have appeared on a YouTube video released by the Sunni extremist group ISIS, calling for others to join their cause.
The men, named as Abu Yahya ash Shami and Abu Nour al Iraqi, are joined in the video by several others who identify themselves as British
"Hello my brothers in Australia," said Shami. "This is the message I want to send to you. From a Muslim brother's heart to another brother's heart."
"Look and see and wake up and understand why this happening," the man identified as Shami said. "Wake up. Wake up and be part of this effort."
The video was uploaded to YouTube on June 19, 2014, and removed by the company soon after.
The second man. identifying as Australian, Abu Nour al Iraqi, also spoke to the camera saying there were plenty of reasons to 'come to Jihad'.
"All thanks and praise be to God. He gave me this chance and gave this chance to many other travellers to come to bilad al sham (region of Lebanon, Syria and Jordan) and if God willing we are going to be successful."
Prime Minister Tony Abbott says the government is redoubling its efforts to stop Islamist extremists who have fought in Syria or Iraq from entering Australia.
"These people should have no place in our country, and we will do our best to keep them out," he said.
"If they can't be kept out, they will be taken into detention because we are not going to allow people who are an obvious threat to our safety and security to roam loose in Australia."
Australia can't have "trained killers who hate our way of life, who hate us, making mischief with the potential to cause mayhem in our country", he said.
The government believes about 100 Australians had fought or were still fighting with opposition groups in Syria and beyond - and some had moved from supporting moderates to backing extremists such as Islamic State of Iraq and the Levant (ISIL, also known as ISIS).
The Sunni militant group has taken over key cities in northern Iraq and is in striking distance of the capital Baghdad, with Canberra worried Australians may now be involved in the fighting.