SINGAPORE - No one can guarantee that Singaporeans will not be affected by the threat of extreme terrorism, said Defence Minister Ng Eng Hen in a Facebook post on Tuesday.

He was writing in response to an incident on Monday in which staff and customers of a Sydney cafe were held hostage by a gunman for 17 hours. The gunman and two other people died in the incident and at least four others were injured.

"We must not allow any person or group to weaken or fracture the strong ties that we have painstakingly built to forge a harmonious multi-racial and multi-religious nation in Singapore," Dr Ng said, adding that he was saddened by the loss of lives in the incident in Australia.

He was reiterating a point he made last month during a closed-door dialogue session with 300 religious and community leaders of various faith.

He was glad to have met them as the attack showed "how even one person can inflict much harm to society".

Dr Ng said during the meeting, he was reassured that leaders of different faiths and backgrounds here understood that "we must come together to support and protect each other" in the event of any incident.