SINGAPORE - Prime Minister Lee Hsien Loong on Saturday said the ongoing conflict in Syria and Iraq has seen terrorist elements in Southeast Asia regrouping and getting more active.

And it was naive to think that Singapore can keep its head low and the threat will pass.

The Government had to do what was necessary to protect Singapore, he told around 300 religious and community leaders from various faiths and groups at the start of a closed-door dialogue with five other ministers on Singapore's concerns with the conflicts in both Middle Eastern countries.

"The threat of terrorism can cause doubts and sow divisions among communities, but we have avoided this danger because our people are rational, they have looked at facts squarely and forthrightly condemned extremists," he said.

Similar dialogues, involving briefings by Singapore's security agencies, have been held since the Sept 11, 2001 terror attacks on the United States and the discovery of a Jemaah Islamiah (JI) cell planning attacks in Singapore later that year.

They cover areas not made public, but which would help community leaders better understand what was happening and the Government's thinking and actions, Mr Lee said.

The last dialogue was in 2011, when JI was reviving its regional network, and since then, Osama bin Laden has been killed and successful counter-terrorism operations have neutralised some groups. But the threat has worsened recently, he added.

Mr Lee spoke in Malay, Mandarin and English, while Foreign Minister K Shanmugam spoke in Tamil.

Mr Lee noted that thousands of fighters from across the globe had flocked to ISIS, including hundreds from Southeast Asia, where former JI leader Abu Bakar Bashir had sworn allegiance to ISIS and his followers had given funds and support to the group.

Malaysia had also put out a White Paper on its strategies to tackle its citizens who returned after joining the group.

Several Singaporeans had also become radicalised, and a few have gone to Syria and Iraq.

Extremist terrorism, Mr Lee noted, could easily disrupt trust and harmony in Singapore's multiracial society.

And doing what was necessary, he said, included getting the support of the community, being vigilant domestically, and "taking swift action to neutralise threats to Singapore, or people who may get themselves in trouble".

Singapore has also contributed to the international effort to tackle the threat at its source, he noted.

The Singapore Armed Forces is joining over 60 other countries, including Muslim countries, in the coalition to fight against the terrorist group ISIS, and sending liaison and planning officers, a tanker aircraft for refuelling, and an imagery analysis team.

Mr Lee added that he appreciated how Singaporeans and the community and religious leaders had responded to the terrorist threat.

He said he was particularly grateful to the Malay-Muslim community, and highlighted the work of the Mufti and the Religious Rehabilitation Group(RRG), who have "done a lot to counter the ideological propaganda of ISIS."

The RRG, religious leaders who counsel terror detainees, have put out brochures and online videos pointing out why ISIS' brutal methods are against Islamic teachings.

At the same time, Muslim groups as well as organisations like the Singapore Buddhist Lodge, Taoist Federation and Bright Hill Temple have chipped in to help Syrian refugees.

Also present at the dialogue were Deputy Prime Minister and Home Affairs Minister Teo Chee Hean, Defence Minister Ng Eng Hen, Communications and Information Minister Yaacob Ibrahim and Culture, Community and Youth Minister Lawrence Wong.

"There are things we can do in Singapore but eradicating terrorism will be a difficult and long-term fight, and we have to continue doing it," Mr Lee said in his speech.

"Provided we work together and be open with each other and share and come close, we will prevail."