By exhorting others on Facebook to fight for the Islamic State in Iraq and Syria (ISIS), radical ideologue Zulfikar Mohamad Shariff "sat on an armchair in Australia and flagrantly sacrificed the lives of the gullible", said Minister for the Environment and Water Resources Masagos Zulkifli yesterday.

That was reprehensible and irresponsible, said Mr Masagos in a Facebook post on Zulfikar, whose detention under the Internal Security Act was announced yesterday.

Mr Masagos was among several ministers and community leaders who commented on Zulfikar's arrest, saying it highlights the danger of terrorist ideology spreading on social media.

Said Minister for Communications and Information Yaacob Ibrahim: "No country can fully block the Internet and prevent what comes in. What is more important is the resilience and cohesion of the nation and our people."

Dr Yaacob, who is also Minister- in-charge of Muslim Affairs, said that Singaporeans must be alert to those who seemingly support terrorism in whatever form.

This is because quick action by citizens to report any potential threats to the authorities is critical for combating the spread of extremism.

Singaporeans should also not hesitate to condemn terrorist groups that employ violence in the name of Islam, he added.

Zulfikar was also denounced as a wolf in sheep's clothing by several Muslim leaders.

Said Mr Masagos: "His radical view of Islam is cloaked with quotes that looked religiously sound to those looking for answers to life."

He urged Muslim Singaporeans to be wary of such views that appear sound but find little traction with most Muslim scholars.

Instead, they should confer with properly qualified scholars who have always stressed the importance of resolving conflicts in a peaceful manner, he said. "We should immediately... turn away from those who incite anger and violence in every sentence they post."

Dr Nazirudin Mohamed Nasir of the Islamic Religious Council of Singapore, said the path to radicalisation begins with sympathising with radical ideologies.

"We must always seek answers from credible sources. This becomes even more important when information is readily available from open sources such as the Internet and social media," he said.

Minister for Family and Social Development Tan Chuan-Jin pointed out that "it's one thing to not support the government of the day but it's another to undermine one's own country".

He added: "To seek to establish radical ideology here is to destroy the very basis of what we exist for - which is to build a Singaporean Singapore, regardless of race, language or religion."

Community leaders also said it was important to speak out immediately against extremist posts and false teachings.

Responses should be loud, said Association of Muslim Professionals chairman Abdul Hamid Abdullah. "If you're confident it is not Islam, correct it on the spot. If you remain silent, your inaction may contribute to the dissemination of wrong information."

Mr Ahmad Tashrif Sarman, 29, assistant secretary of the Bukit Batok Inter-Racial and Religious Confidence Circle, said every bit of response to such social media posts helps. "If we leave them alone, they become more radical."

Culture, Community and Youth Minister Grace Fu called on Singaporeans to stay united and not let extremism poison the relations between people of different religions.

"Let's stand together with our Muslim friends, as one united people, to keep Singapore safe for all," she wrote on Facebook.

Bishop Wee Boon Hup, vice-president of the National Council of Churches Singapore, said: "Most Singaporeans, whether of faith or not of faith, know this is the view of a few disaffected individuals."

Inter-faith relations here are strong, he added. "Over the years, we have built enough trust in each other to weather this kind of event."