SINGAPORE - Singaporeans must always be vigilant and "never let down our guard" against the threats posed by extremist terrorism, said Defence Minister Ng Eng Hen.

In a Facebook post on Wednesday, Dr Ng noted how several events in Malaysia serve as reminders for the Republic to be vigilant about its security.

He cited how the Malaysian Police Special Branch Counter-Terrorism Director told the press in a special briefing on the ISIS threat on April 2 that it was not a matter of if Malaysia will be attacked, but when.

Dr Ng also flagged how 17 individuals were detained in Malaysia on April 5.

They were plotting to attack police stations and army camps to obtain firearms, and planning to make bombs based on detailed notes allegedly from Imam Samudra, an Indonesian who was executed for his role in the 2002 Bali bombings.

The group was also planning to kidnap high-profile individuals, and some had received training in Afghanistan and Indonesia's Sulawesi province.

That was the third reported ISIS-related terrorist plot foiled by the Malaysian security forces, and the Malaysian government is increasingly concerned about the terrorism threat posed by ISIS and its sympathisers, Dr Ng wrote.

He noted that 92 individuals have been arrested for terrorism-related offences since 2013. There were also other arrests for terror recruitment and financing, and attempts to travel to Iraq and Syria.

To guard against those threats, Singapore must also maintain its social defence, "led by community and religious groups to maintain racial harmony", he said.

Dr Ng added: "As we did before against threats from Al-Qaeda and Jemaah Islamiyah, we will overcome by remaining united and vigilant."