Australia will be “utterly unflinching” in the fight against Islamic State at home and abroad, Tony Abbott has told world leaders.

Addressing a special United Nations Security Council session on the foreign fighter terrorist threat, Mr Abbott said IS had declared war on the world.

“Whatever they think or say, terrorists aren’t fighting for God or for religious faith. At the heart of every terrorist group is an infatuation with death,” he told the meeting chaired by US President Barack Obama.

It is only the second time in history a US president has chaired the council.

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At the start of the meeting, Mr Abbott threw Australia’s support behind a US-drafted resolution mandating a global crackdown on foreign fighters.

The legally binding resolution passed unanimously, winning support from all 15 UNSC members.

He expressed regret that dozens of Australians had succumbed to the IS “delusion” but made it clear the government would not go easy on them.

“The Australian government will be utterly unflinching towards anything that threatens our future as a free, fair and multicultural society,” he said.

“A beacon of hope and exemplar of unity-in-diversity.”

He congratulated Mr Obama on his leadership against IS and said Australia was now poised and ready to help in military operations in Iraq.

“Our goal is not to change people but to protect them; it’s not to change governments but to combat terrorism,” he said.

Despite the dark times, there were grounds for hope: not least the all-but-universal revulsion that IS’s crimes had generated around the world.

“Perhaps the realisation is now dawning for all peoples, all cultures and all faiths that it can never be right to kill in the name of God.

“That would be a moral victory far surpassing any military success.”

Mr Abbott’s speech came amid a series of one-on-one meetings with world leaders including Obama, Indonesia President Susilo Bambang Yudhoyono, Japanese Prime Minister Shinzo Abe and French President Francois Hollande.

He will address the UN General Assembly on Thursday.