SYDNEY (REUTERS) - Australia has issued arrest warrants for a pair of Australian citizens believed to be fighting in Syria, the Australian Broadcasting Corporation (ABC) reported on Tuesday, after images emerged of the two holding the severed heads of Syrian soldiers.

Australian Federal Police counter-terrorism chief Neil Gaughan told the ABC in an interview that warrants had been issued for Australians Khaled Sharrouf and Mohamed Elomar on terrorism offences.

A Twitter account linked to Al-Qaeda offshoot Islamic State in Iraq and Syria last week published grizzly pictures of the beheaded corpses and heads of five soldiers killed in Syria's Raqqa province, saying the soldiers were from the 17th division.

Sharrouf and Elomar travelled to Syria and Iraq late last year, the ABC reported, and late last week a Twitter account purported to belong to Sharrouf showed pictures of Elomar handling severed heads.

"As soon as they set foot on Australian soil they will be taken into custody," Mr Gaughan said.

Australia has raised the alarm about the number of its citizens believed to be fighting alongside insurgents overseas, including an Australian suicide bomber who killed three people in Baghdad this month.

That has added to concern about radicalised fighters launching attacks when they return home, a threat the government has used to justify a package of major new intelligence legislation.

Last week, Attorney General George Brandis announced sweeping national security reforms that would make it easier to track Australian citizens believed to have fought overseas both while they were abroad and after they returned home.

Mr Brandis told the ABC that concrete evidence had now emerged to support those concerns.

"There is evidence that they are trained in terrorist tradecraft to perform acts of domestic terrorism in the event that they return either to their home countries or go elsewhere after they have been in theatre," he said. "So that is a new and very alarming development."