Singapore has barred two foreign Islamic preachers from entering the country to preach during religious-themed sea cruises, the interior ministry said Monday.
The pair had earlier applied to preach in the city-state but their applications were rejected. However authorities later learned they planned to preach aboard cruise ships in late November.
"They will not be allowed to get around the ban by preaching instead on cruise ships which operate to and from Singapore," the Ministry of Home Affairs said.
One of the preachers, Ismail Menk, "has been known to preach segregationist and divisive teachings" while the other, Haslin bin Baharim, "has expressed views that promote disharmony between Muslims and non-Muslims", it said without giving their nationalities.
Singapore also on Monday banned four foreign Islamic books containing what it called "undesirable and harmful teachings".
The information ministry said the books' teachings "can cause social distancing, distrust, hatred and even violence among people of different faiths and religious views" in the ethnically diverse nation.
Possession, distribution and failure to surrender copies of the books to the police will be an offence effective Tuesday, it said.
"The threat of extremism is real and should not be taken lightly," said Information Minister Yaacob Ibrahim.
"The government strongly condemns the use of such publications to espouse destructive ideologies and promote enmity between communities."
The books were published in Indonesia between 2011 and 2016.
Singapore's move comes amid attempts by the Islamic State (IS) group to establish a base in Southeast Asia.
IS-backed militants, including several foreign fighters, seized the southern Philippine city of Marawi in May as part of plans to establish a caliphate, sparking a bloody five-month campaign by Filipino troops to dislodge them.
The top US commander in the Pacific, Admiral Harry Harris, earlier this month warned against the threat posed by Southeastern Asian militants returning to the region as IS loses ground in Iraq, Syria and Libya.
"Foreign fighters are passing their ideology, resources and methods to local, homegrown, next-generation radicals," Harris had said in a speech in Singapore.
"So we must stop ISIS at the front end and not at the back end when the threat can become even more dangerous," he said, using another name for IS.
Singapore in 2001 arrested several suspected militants and foiled a plot to bomb several foreign targets in the country, including the US embassy.