Australian police have issued arrest warrants for two Australian Islamic State fighters after one of them is pictured online brandishing the severed heads of Syrian government soldiers.
The two suspects have been identified by Australian police as Khaled Sharrouf and Mohamed Elomar.
They are thought to be with the radical Islamic State fighters in Syria.
Photographs posted on social media showed Elomar holding severed heads in his hands, and he boasts that he would cut the throats of infidels.
The two men from Sydney are considered to be the two most notorious Australians fighting with the Islamic State in Syria and Iraq.
Neil Gaughan, Australia’s deputy federal police commissioner, said the two are now wanted on terrorism-related charges.
“Words don't adequately describe how abhorrent those photographs are," Gaughan said.
"In 30 years of policing, it is probably one of the worst things, if not the worst thing, I have seen. The Australian government, rightly so, came out very strongly on Friday criticizing in the very strongest possible terms the type of behavior that those two gentlemen are allegedly involved in," he said.
"(We) can assure the Australian community that we have current first instance warrants for their arrest and as soon as they set foot on Australian soil they will be taken into custody," Gaughan said.
It is understood that Elomar and Sharrouf had links to a teenager from the Australian city of Melbourne.
Authorities said that 18-year old Adam Dahman blew himself up in Baghdad in a suicide bombing that killed five people last week.
Dahman was questioned by Australia’s intelligence agencies before he flew to the Middle East last year. But authorities say they had insufficient powers to stop him from leaving the country.
In Canberra, the government is preparing new laws that would make it easier to prosecute terrorism cases.
Australia Attorney-General George Brandis said there is a small, yet dangerous, group of homegrown extremists in his country.
“The one thing no Australian should ever think is that this is a problem that exists on the other side of the world, because while it may take shape on the other side of the world, the number of Australians who are participating in this war fighting in Syria and Iraq shows that this is a problem that exists and germinates within our suburbs, within the suburbs of Sydney and Melbourne and Brisbane, among a very small number of people - a very, very small number of people - but nevertheless, this is a product which has a domestic germination," Brandis said.
The Australian Security Intelligence Organization wants greater powers to monitor the phones and emails of terrorism suspects.
Organization Director-General David Irvine said, "We've always been worried about the threat of home grown terrorism. In the last 10 years we have actually stopped four mass casualty attacks occurring in Australia when we stopped them quite early in their planning stages."
The government estimated that there are 150 Australians fighting with radical groups overseas.
Richard Barrett is a former British diplomat and senior vice president of the strategic intelligence provider The Soufan Group, which advises governments on security and intelligence matters.
Barrett said the concern is that Western fighters in Iraq and Syria will carry out atrocities when they get back home.
“There has been a man, a Frenchman, who went back to Europe and killed four people outside the Jewish museum in Brussels not very long ago," Barrett said.
"He had been with the Islamic State, or the Islamic State in Iraq and Syria as it was then, for about a year beforehand. So clearly even if it is not radicalizing people to that point, their participation in that fight clearly it is attracting people who could very well commit terrorist acts back in their home countries, and I think that, you know, is a very legitimate concern," he said.
Muslim groups in Australia said that organizations such as the Islamic State are winning over young people, thanks to slick online propaganda campaigns.