At least three Singaporeans are known to have travelled to Syria to join the Islamic State in Iraq and Syria (ISIS) terror group, two of them with their families.

In its latest Singapore Terrorism Threat Assessment Report, released at the end of last month, the Ministry of Home Affairs (MHA) said there are no indications that Haja Fakkurudeen Usman Ali, 42, and Maimunah Abdul Kadir, 50, intend to return to Singapore.

The third, Megat Shahdan Abdul Samad, is believed, based on available information, to have been killed, the report said.

Megat, who would have been 40, was featured in two ISIS propaganda videos in 2017.

Maimunah, who is married to a Malaysian, travelled to Syria with her two Singaporean children from a previous marriage.

Haja, who was a manager in a local supermarket, is a former Indian national who received Singapore citizenship in 2008 and travelled to Syria in 2014 with his Singaporean wife and three children.

The Singapore Constitution allows a naturalised citizen to be deprived of his citizenship if "he has shown himself to be disloyal or disaffected towards Singapore", or has "been engaged in any activities which are prejudicial to the security of Singapore".

An Indian national and former Singapore PR who abetted and assisted Haja, system analyst Gul Mohamed Maracachi Maraicar, was investigated in 2014. He was deported and banned from entering Singapore for his role in abetting and aiding Haja.