SYDNEY (Reuters) - The children of refugees who fled Lebanon's civil war for peaceful Australia in the 1970s form a majority of Australian militants fighting in the Middle East, according to about a dozen counter-terrorism officials, security experts and Muslim community members.

Of the 160 or so Australian militants believed to be in Iraq or Syria, several are in senior leadership positions, they say.

But unlike fighters from Britain, France or Germany, who experts say are mostly jobless and alienated, a number of the Australian fighters grew up in a tight-knit criminal gang culture, dominated by men with family ties to the region around the Lebanese city of Tripoli, near the border with Syria.

Not every gang member becomes a radical and the vast majority of Lebanese Australians are not involved in crime or in radicalism of any sort. Australian Muslims say they are unfairly targeted by law enforcement, especially after the surge in fighting in Iraq and Syria, and that racial tensions are on the verge of spiralling out of control.

Still, there is a clear nexus between criminals and radicals within the immigrant Lebanese Muslim community, New South Wales Deputy Police Commissioner Nick Kaldas told Reuters. "It is good training," said Mr Kaldas, himself an immigrant from Egypt and a native Arabic speaker.

The ease with which some hardened criminals from within the community have taken to militant extremism, and the prospect of what they will do when they return home from the Middle East battle-trained, is a major worry for the authorities, he said.

Mr Kaldas oversees the state's Middle Eastern Organised Crime Squad and was the United Nations-appointed chief investigator into the assassination of former Lebanese prime minister Rafic Hariri in a car bomb attack in Beirut in 2005.

In recent years, he said, the divide between criminal gangs and radicals in Lebanese community, who were driven by different motives, had narrowed. "I do worry about those who may be extremists infecting more people who were just pure criminals," said Mr Kaldas.

Prime Minister Tony Abbott says that at least 20 of the fighters are believed by authorities to have returned to Australia, and that more than 60 people believed to be planning to go to the Middle East have had their passports cancelled.

Last month, the national security agency raised its four-tier threat level to "high" for the first time and about 900 police launched raids on homes in Sydney's predominantly Muslim western suburbs and in Brisbane.

Only about half a million people out of Australia's 23.5 million are Muslims, making them a tiny fraction in a country where the final vestiges of the "White Australia" policy were only abolished in 1973, allowing large scale non-European migration.

At least half of Australia's Muslims live in Sydney's western suburbs, which were transformed in the mid-1970s from white working-class enclaves into majority-Muslim outposts by a surge of immigration from Lebanon.

The inhabitants of low-slung suburban villages like Lakemba, which now hosts the Imam Ali Mosque, Australia's largest, soon replaced the greasy aroma of fish and chips - and beer - with the scent of grilled meat and cardamom, the staples of the Middle East.

A broad sampling of the areas in Sydney most associated with Lebanese ancestry on the 2011 national census - Auburn, Lakemba, Punchbowl, Granville - show them lagging far behind the rest of New South Wales state on indicators such as income and employment.

After the raids and an intense media focus on the community, most Lebanese Australians are wary of public comment. In the western suburbs, outsiders are looked on with suspicion and few were willing to speak to reporters.

"It's a troubled community as a group," said Mr Greg Barton, director of the Global Terrorism Research Centre at Monash University. "So they're over-represented in petty crime, in organised crime, in religious extremism."

When the civil war erupted in Syria in 2011, the fighting was a draw for many Lebanese Muslim families in Australia. Clannishness and old family networks made it easy for youngsters from the community to slip away and join the fighting.

"You had people from the neighbourhood and you flew into Tripoli or flew into Beirut and drove up to Tripoli and were taken across," Mr Barton said. "It was a very smooth, easy pathway in."

Both the police and academics, however, struggle to explain what would draw second-generation Australians back to the violence which their parents had fled.

Mr Aftab Malik, a Scholar-in-Residence at Sydney's Lebanese Muslim Association who has spent years living in western Sydney's Muslim community, said he believed the convergence between radical Islam and organised crime was unique to Australia. "I haven't come across that in the United States or in Great Britain. It's quite specific here and I don't know why that is," he said.

The fighters from Australia include a radical using the name Abu Sulayman al-Mujahir, who left for the Middle East with what intelligence officials say was the task of ending an internecine war in Syria between Al-Qaeda and the Islamic State of Iraq and Syria (ISIS), and a suicide bomber who killed three people in Baghdad in July. ISIS named the bomber as Abu Bakr al-Australi on its Twitter feed.

It also includes two men from Sydney, Khaled Sharrouf and Mohamed Elomar, who have posted images from Syria on Twitter, showing them posing with the heads of executed fighters, holding guns and standing over bloodied bodies.

Australia has issued warrants for their arrests, but police say they are still believed to be in the Middle East. Their social media accounts have been suspended.

Elomar's brother is serving jail time for assaulting a police officer, while Sharrouf served four years for his involvement in a 2005 plot by Islamist radicals to blow up a nuclear power plant in Victoria state.

"They were stand over men, any everybody knew it, and that's it," Lebanese Muslim Association president Samier Dandan said during a drive through western Sydney, using an Australian term for an extortionist or violent thug.

For Mr Muhammad, a young man of Lebanese ancestry who grew up in the western suburbs of the city, the evolution from hard man to militant makes perfect sense.

"We tend to live in these clusters, and so when media or government or any outside organisation or group of people say'look at them' - we come together," he said, describing a"siege" mentality within the community.

Although not involved in crime or extremism, Mr Muhammad, who refused to give his surname, said he knew people who were.

A schoolfriend, he said, was involved in criminal gangs as soon as he left high school and was killed in fighting in the Middle East earlier this year.

Over the past year or so, Mr Muhammad said, his cousin, who has been jailed for assault and who used to drink alcohol and never prayed, had shaved his head and grown a long beard. He also began sharing violent jihadist videos on social media.

"The violence stays, it's just that you're doing it for a purpose this time," he said of those who fight alongside ISIS or other groups in Syria and Iraq.