SINGAPORE - Singapore has been fortunate to be spared from a terrorist attack so far, but what happens when the terrorists get through?

Prime Minister Lee Hsien Loong in his National Day Rally speech on Sunday night took on the sombre reality of the growing threat of terrorism, and the consequences an attack might have on social cohesion.

"If the terrorists are from abroad, it may be easier for us to stand together. But if the terrorist turns out to be a Singaporean - one of our own, like what happened in Nice where the truck driver was French - our multiracial society will come under enormous strain," he said.

People in countries hit by terrorist attacks have reacted in two possible ways: with shows of solidarity, or with mounting fear and distrust, sparking a rise in racial attacks.

When Paris was rocked by a series of terrorist attacks last November, Parisians banded together, offering shelter and free rides to strangers and donating blood at hospitals. But tensions boiled over too, with mosques and Muslim shops vandalised, and Muslims - especially women and girls in religious attire - were physically attacked.

"The question is: which will happen in Singapore?" asked Mr Lee. "It comes down to our collective resolve to stand with each other. That in turn depends on how well we have prepared ourselves before an attack. To build trust, to strengthen bonds, to maintain and expand our common space, so that we feel instinctively one people."

A big plus, he said, is that religious and community leaders here have taken courageous stands, condemning terrorist attacks and refuting extremist views. They make clear that terrorists do not represent Islam, or Singapore Muslims, and lead by example, guiding their communities to stand together.

"They also understand that ours is a multiracial society. There has to be give and take. Each community has to engage and understand each other, and not segregate itself from other communities. We have to respect one another's religions. We cannot treat other groups as infidels," he said. "If religious groups take an exclusivist approach and discourage interaction and contact with others, we will deepen our fault lines."

But some foreign preachers visiting Singapore do not understand the country's multiracial context and want to preach their exclusivist practices and doctrines here, said Mr Lee.

"That would cause us serious problems. From time to time, we have banned such preachers from entering Singapore - Christian, Hindu and also Muslim preachers."

Muslim leaders here have expressed concerns about such Muslim preachers, noted Mr Lee.

"I'm glad that they are vigilant, making sure that the Islam preached and practised in Singapore suits our multiracial context."

That is why the Islamic Religious Council of Singapore (Muis) and the Singapore Islamic Scholars and Religious Teachers Association (Pergas) have the Asatizah Recognition Scheme to endorse Islamic religious teachers here.

During his speech, Mr Lee supported a call by Muslim leaders to make the scheme - which is currently voluntary - mandatory instead. All religious teachers, or asatizah, will have to register.

And beyond social cohesion and religious understanding, Singapore is also buffing up its community response.

"Our diplomats and security forces, the Home Team and SAF (Singapore Armed Forces), are doing excellent work, but they alone cannot guarantee our security and safety, or hold us together," said Mr Lee. "All of us must do our part."

He will launch the SG Secure national movement next month.

"It is a call to action to all Singaporeans. To be sensitised, trained and mobilised to protect our society from a terrorist attack," he said. "Ultimately, what matters most is our resolve to hold together and fight to defend our place in the world."