A scheme that endorses Islamic religious teachers in Singapore will be made mandatory from Jan 1 next year, with all religious teachers required to register in the Asatizah Recognition Scheme.

But the asatizah will be given a one-year grace period to obtain the necessary qualifications, which include at least a diploma in Islamic studies from a recognised institution, Minister-in-charge of Muslim Affairs Yaacob Ibrahim told reporters at the National Day Rally, after Prime Minister Lee Hsien Loong spoke in his Malay speech of the need to strengthen the scheme.

Started in 2005, the scheme is voluntary now, with about 80 per cent of asatizah here on its register.

But the Islamic Religious Council of Singapore (Muis) will work with the Asatizah Recognition Board and the Singapore Islamic Scholars and Religious Teachers Association to make it mandatory.

Muslim leaders had proposed ways to make the scheme stricter, amid reports of Singaporeans radicalised by extremist ideology. They did it most recently at a closed-door dialogue with Dr Yaacob, who is also Minister for Communications and Information, and Environment and Water Resources Minister Masagos Zulkifli on Saturday.

In welcoming it yesterday, Mr Lee said: "I commend the Malay/Muslim community for taking the initiative to deal with a sensitive problem. These measures will ensure that all asatizah in Singapore understand how Islam is practised here, and can guide their students to live in harmony with fellow Singaporeans of all races and religions."

Dr Yaacob told reporters the 20 per cent who have yet to register belong to private schools and centres, or run their own classes. They include older teachers who have been doing it for decades.

"Some of them also fear they may not have the necessary qualifications," he said. "We'll work with them to see what we can do in terms of courses to ensure they'll qualify under the scheme."

Mufti Fatris Bakaram said the scheme was important amid rising demand for religious classes too.

"There must not be any gap where people who are not qualified can take advantage of the system, claiming it is just a voluntary initiative," he said.

In his speech, Mr Lee said it was critical for Singapore's asatizah to understand the country's multiracial context. All religions here practise their faith in a multiracial and multi-religious context, he said.

The different groups here respect each other's faiths, make practical compromises to accommodate one another, and do not segregate themselves from other communities.

"But it is not so in many other countries. It may be the same religion, but the practice and teaching vary from country to country. And sometimes, these practices and teachings are exclusivist and intolerant," said Mr Lee.

Some foreign preachers visiting Singapore do not understand the country's multiracial context, too.

"They preach separation between believers and non-believers. They condemn those who practise other faiths, and sometimes even those who practise the same faith, but in different ways," said Mr Lee.

"They advocate practices and customs that would cause grave harm in Singapore."

Singapore has, from time to time, stopped such preachers - of all faiths - from entering the country.

"The Government has to be consistently firm no matter what the religion, in order to safeguard our religious harmony."