Police are investigating a specific threat made against an Australian newspaper by a Melbourne man believed to be fighting with terrorists in Syria.

Suhan Rahman, 23, is thought to have been in the war-torn nation for five months, according to media reports.

It is not clear if he joined Islamic State fighters but photos on social media under the account Suhan Abdul Rahman appeared to show him in Syria.

His Facebook account contains messages of support for the Charlie Hebdo gunmen and threats to "spill blood" in Australia.

Victoria Police are investigating the threats, with a particular focus on this post: "theres no good left in u if none of u do something about the australian newspaper mocking our prophet peace be upon him. Dont be cowards (sic)."

The posting makes explicit, graphic suggestions which the ABC has decided not to publish.

Victoria Police said it was working closely with the company named in the threats.

Additional security measures have been put in place at News Corporation in Melbourne.

No activity has been registered on the Facebook account since late yesterday morning.

In a statement, Victoria Police said it was concerned about the small number of Australians who had travelled to Syria and become embroiled in extremist ideologies.

It said it was continuing to monitor the situation closely.

While Federal Minister for Border Control Peter Dutton would not comment on the specifics of this case, he told reporters the National Security Committee of the Cabinet was working with intelligence and security agencies on these kinds of matters.

"The Prime Minister has been absolutely rock solid in dealing with these issues. The Government will do whatever it takes to keep Australians safe," he said.

Opposition Leader Bill Shorten was also reluctant to talk specifics, opting instead to send a message to Australian youths.

"Any young people, disaffected, who are attracted to these crazy causes in Iraq, Northern Iraq and Syria - don't go," he said.

"We don't think this young man represents anywhere near the rest of the Muslim Australian community."

Parents should look out for warning signs of radicalisation: expert

This case is just the latest involving young radicalised Muslim men in Melbourne.

In September, Numan Haider, 18, stabbed two policemen before being shot dead outside the Endeavour Hills police station in Melbourne's south-east.

He had taken to radical Islam in the months before his death and authorities had taken his passport away from him.

Global terrorism expert, Professor Greg Barton from Monash University, said seemingly normal young people could be radicalised quickly.

He said there were patterns that parents could look for including sudden adoption of extremist ideas or even a new group of friends.

"They're appealing to the subculture of their new peers," he said.

"It is possible to turn kids around. This is basically peer influence but once a kid is on a plane to Turkey and a bus to Syria it's really hard to help them.

"Then they're a danger to others and a danger to themselves."

Suhan Rahman's family has reportedly urged him to return home.

Victoria's Acting Premier James Merlino said the Government was considering what more could be done to stop young Muslim men becoming radicalised.

"Addressing these problems before it gets out of hand is absolutely crucial and we do need to see if there are further things that we can do that we're not doing at the moment," he said.