Opening the 27th ASEAN Summit here today, Datuk Seri Najib Razak delivered a hard-hitting speech against extremism and terrorism, stressing that new solutions had to be found to address the problem.

Speaking in front of leaders from across Southeast Asia, the Malaysian prime minister said military might alone would not be enough to defeat those who were bent on causing war, mayhem and death as well as desolation and despair.

"It is the ideology propagated by these extremists that is the cause of this sadistic violence, and in this time of tragedy we must not lose sight of the fact that the ideology itself must be exposed as the lie that it is - and vanquished.

"For it is not Islamic. It cannot be," said Najib, who is the 2015 ASEAN chairman, in the speech delivered at the Kuala Lumpur Convention Centre (KLCC) here.

The prime minister had started his speech by referencing the many innocent lives lost due to terror acts in places like Paris, Beirut, Sinai, southern Philippines and Mali.

Malaysian national Bernard Then, 39, was reported to have been beheaded at the Abu Sayyaf remote stronghold in Jolo, Sulu Province, about 1,400km south of Manila.

Then, an electrical engineer from Sarawak, and a woman, Thien Nyuk Fun, 50, were abducted by four armed men who raided the Ocean King Restaurant in Sandakan at 7.45 pm on May 14.

Meanwhile, militant group IS has claimed responsibility for a number of terror acts, including the attacks against Parisian targets on Nov 13 that killed over 100 people.

Touching on the atrocities committed, Najib said: "Suicide - under any circumstances, never mind suicide bombing that kills the innocents - is a terrible sin."

The prime minister noted that it was worth examining why anyone should be misguided enough to follow this perverted ideology.

"What is their motivation? But let us be clear - it's an utter travesty of a religion of peace, justice and moderation," said Najib.

The Malaysian leader is an ardent advocate of the moderation concept, having brought up the matter on the global stage, including at the United Nations General Assembly.

And it was no different at the ASEAN gathering, as he said: "More than ever, it's the last concept, moderation, that we're in dire need of around the world.

Moderation or 'wasatiyah' is at the heart of Islam.

He stressed that it was a Quranic injunction that no Muslim could disobey.

"But moderation does not only belong to us. It has been the locomotive of the non-violent approach to solving conflict throughout history," Najib said.