Interior Minister Teo Chee Hean said returning fighters have the skills to carry out terror attacks or support others planning them.

"The presence of former foreign fighters in our region - whether they originate from Southeast Asia or elsewhere -- is a security threat to us," Teo told parliament.

"This threat is magnified if these returnee fighters are Singaporeans."

Teo cited parallels to the threat posed by foreign fighters who returned to Southeast Asia after fighting in the Afghan war against the Soviets in the 1980s.

He said several members of the Jemaah Islamiyah terror network arrested in Singapore in 2001 for planning attacks on US and other foreign targets in the city-state had trained in Afghanistan.

Teo also said that a Frenchman suspected of carrying out a deadly shooting at the Jewish Museum in Brussels in May had travelled through Thailand, Malaysia and Singapore, most likely "to mask the fact that he was a returnee from Syria".

He said local authorities detained a Singaporean in October 2012 after he attempted to travel to Syria "to engage in armed jihad".

Two others have had their movements restricted after their attempts to contact militant groups fighting in Syria were detected.

The government is aware of two Singaporeans currently fighting in Syria along with their families, Teo said.

Governments around the world have expressed concern at the flow of foreigners to the Syrian conflict, with the New York-based intelligence firm Soufan Group estimating some 12,000 have done so in the past three years.