SINGAPORE - Defence Minister Ng Eng Hen said on Sunday (June 5) that a "gathering storm" of terrorism has real potential to destabilise the region, as he called for close cooperation among countries to fight the threat.

"Terrorists have capitalised on existing smuggling routes to move people and arms in the region that include Southern Philippines, Indonesia, Malaysia and Singapore," Dr Ng said in an address to defence ministers, officials and scholars from 35 countries at the annual Shangri-La Dialogue security forum.

He noted that the four South-east Asian nations have suffered terror attacks or foiled terror plans in recent years, adding: "The threat will grow if terrorist groups become more organised to mount sophisticated, large-scale attacks with deadlier weapons.

"This gathering storm has the real potential to destabilise this region, if not tackled decisively and together."

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He suggested that countries combine their resources for anti-extremism operations, citing proposed patrols in the Sulu Sea, in south-western Philippines, by Malaysia, Indonesia and the Philippines to counteract maritime terrorism and smuggling as one such initiative.

And last month, he noted, some 3500 troops, 18 naval vessels, 25 aircraft and 40 Special Forces teams from 18 countries including the US, China, India and Japan participated in the Asean-led ADMM-Plus Maritime Security and Counter-Terrorism Exercise in Brunei, the South China Sea and Singapore.

"Security forces, including militaries of individual countries, will have to combat terrorism rigorously...Collectively, we must work closely together to build up joint responses, and strengthen intelligence, surveillance and reconnaissance efforts," said Dr Ng.

He noted that while the religious pretext of terrorism has not changed, the security situation in the region has evolved since the inaugural Shangri-La Dialogue in 2002. The rise of the Islamic State in Iraq and Syria (ISIS) is fomenting "a deeper and stronger under-current" of extremism.

"In the past three years alone, ISIS has recruited more sympathisers and operatives in Asean than Al-Qaeda did in the last decade, with more than a thousand fighters in Iraq and Syria," said Dr Ng.

"Returned fighters have linked up among themselves through their networks and declared their collective goal to establish a caliphate, motivated by, in Mr Lee’s words, 'a deeply-felt sense of Islamic brotherhood that transcends ethnicity and national boundaries' and 'a shared ideology of universal jihad'," said Dr Ng, quoting late Singapore senior statesman Lee Kuan Yew's speech in 2002 at the first edition of the Shangri-La Dialogue, organised by the International Institute for Strategic Studies (IISS) and the Singapore Government.

But Dr Ng stressed that the war on terror is not a war on Islam.

"Mr Lee reminded then that 'it is necessary to emphasise that the war against terrorism is not a war against Islam'...This battle is against terrorists groups that “have hijacked Islam as their driving force and have given it a virulent twist… [We] must support tolerant non-militant Muslims so that they will prevail,” he said.

The minister was speaking on the final day of the three-day forum, which has been dominated by the South China Sea territorial spat between China and four Asean countries: Vietnam, the Philippines, Malaysia and Brunei.

Tension has been rising over China's reclamation works on disputed reefs in the waterway, which hosts a vital global shipping route. Manila has taken China's claim to the Permanent Court of Arbitration (PCA) in The Hague and a verdict is expected to be out some time in June - but Beijing has said it will not recognised the ruling.

US Defence Secretary Ashton Carter and his counterparts from Britain, France, Canada, and India have all weighed in on the dispute at the forum. In speech after speech, they have called for China to respect international laws and freedom of navigation and overflight in the South China Sea.

Dr Carter warned that China is erecting a "Great Wall of self-isolation" and said the US will stand with its allies in the region to ensure freedom of navigation and overflight in the South China Sea.

China's representative at the Dialogue, Admiral Sun Jianguo, has hit back at the criticisms, saying that China respects international laws and is merely upholding its sovereignty in the South China Sea. He also slammed the US, allies with the Philippines, of double standards and irresponsible behaviour in the waterway.

Dr Ng said of the dispute: "I think all of us are conscious that more is at stake than disputed rocks or islands. As Mr Lee observed in his 2002 speech – 'the competition for economic and diplomatic influence has started'”.

The minister said China has "participated fully" in the regional security architecture, in response to a comment by a Chinese military delegate that it is "dominated by the US and its alliances".

"The Chinese question that the security architecture is not inclusive...is somewhat puzzling," said Dr Ng.

Referring to Asean defence ministers' informal meeting with their Chinese counterpart, General Chang Wanquan, in Laos last month, he added: "[Asean defence ministers] recently met in Laos, with just one plus partner, and that was the Chinese minister Chang.

"[The Chinese delegate]asked how we can make it more inclusive. I’m a practical man, I would like to invite Minister Chang [to the Shangri-La Dialogue]. Please extend our invitiation to Minister Chang."