When he first settled in Australia in 2002, Zulfikar bin Mohamad Shariff was known as a social activist fighting for the right of Singapore schoolgirls to wear the Muslim headscarf.

In an interview with The Age, the newly-arrived Shariff was enthusiastic about his new home. "In Australia you can think independently and speak freely. You don't have that in Singapore," he said.

But when the 44-year-old Australian resident returned to Singapore this month, he was arrested for "terrorism-related activities", which included supporting Islamic State through Facebook posts. It is now alleged that during more than a decade in suburban Melbourne the Singapore-Australian dual national became increasingly radicalised.

After holding him this month under the Internal Security Act (ISA), the Singapore Government ordered Shariff be jailed for two years.

It also accused him of supporting Al-Qaeda and an allied regional group, Jemaah Islamiyah, which was responsible for the 2002 Bali bombings that killed 202 people, including 88 Australians.

Shariff studied international relations at La Trobe University, according to multiple reports.

Property records show that during more than a decade in Melbourne he lived in Glenroy, Springvale and Dandenong South.

Singapore's Ministry of Home Affairs said he "had embarked on the path of radicalism as early as 2001 after reading jihadi-related material".

"While in Australia, he continued to pursue radical ideology by joining the hardline Hizbut Tahrir organisation," it said in a statement.

Hizbut Tahrir is a fundamentalist organisation that preaches a hardline islamist ideology. Though former Prime Minister Tony Abbott threatened to ban the group they remain legal in Australia, though controversial.

"Zulfikar has made use of social media to propagate and spread his radical messages," the Singaporean government statement says.

"He considered his propagation of radical material as a form of jihad, by way of creating awareness of ISIS and promoting armed jihad."

Singapore media has published posts from Shariff's Facebook account, which now appears to have been deleted.

A post from June 2014 reads: "The western media accused ISIS of various atrocities. We should be careful when receiving news from western fasiq (un-Islamic) sources." 

A post from last August states that "ISIS is making good ground" and "may Allah protect the brothers and sisters".

Another post in the same month states: "One day soon, we will run out of excuses. And join the jihad."

The Ministry said Shariff had established and maintained contact with radical preachers in Australia and overseas.

He was arrested on July 1 when he returned to Singapore for a visit.

"He had made several return trips to Singapore between 2002 and 2014," the Ministry said.

"He is still a Singaporean and recently revealed to the Singapore authorities that he had also taken up Australian citizenship.

"Three of his children are also holding dual Singaporean and Australian citizenship.

"His wife and his other children are not Singapore citizens.

According to the Singaporean government, Shariff has been receiving "unemployment benefits from the Australian government" while in Singapore.

In 2002, Shariff made news for defending two six-year-old schoolgirls suspended from Singapore primary schools for wearing the Muslim headscarf.

At the time, he told The Age he had fought the headscarf ban for two years and faced arrest in Singapore for criticising the government.

The same year, he was quoted in the Illawarra Mercury as saying: "I'm out of Singapore to make sure that I don't become a victim of political manoeuvring."

Singapore authorities have detained or repatriated dozens of people in the past year, most of them migrant Bangladeshi workers, for suspected links to militant fundraising.

The Ministry said Zulfikar had contributed to the radicalisation of a man detained under the ISA last year and to that of "a radicalised businessman" who had been placed under a restriction order this month. A restriction order means a person cannot move home, change jobs or go abroad without approval.

"In view of the high level of the terrorism threat that Singapore currently faces, and the global terrorism threat posed by ISIS, Zulfikar's promotion of violence and ISIS and his radicalising influence pose a security threat to Singapore," it said, referring to Islamic State.

Zulfikar had contributed to the radicalisation of a man detained under the ISA last year and to that of "a radicalised businessman" who had been placed under a restriction order this month. A restriction order means a person cannot move home, change jobs or go abroad without approval.

A spokeswoman said Foreign Minister Julie Bishop was aware of Sharriff's arrest.

"Mr. Shariff is an Australian citizen but entered Singapore on a Singaporean passport. As Singapore does not recognise dual nationality, Mr. Shariff is being treated as a Singaporean citizen as per their laws," she said.

"While I will not comment on law-enforcement security matters, I can confirm that our consular officials are seeking to provide assistance to Mr. Shariff".

With Reuters