Washington: US President Barack Obama's address at the start of the international summit on countering violent extremism was perhaps bound to fall a little flat given that he is wedded to the language of nuance and moderation while his foes campaign in vibrant, abhorrent technicolour.

Having appalled and captivated the world with individual beheadings, and aware that it must increase its depravity to maintain our focus, the so-called Islamic State has graduated to mass murder by immolation and beheading.

As Mr Obama addressed representatives of more than 60 nations, including Australia, in Washington, DC, on Wednesday afternoon, reports were circulating that IS (also known as ISIL and ISIS) was now harvesting human organs for sale, while IS in Libya had warned Italy, "the nation signed with the blood of the cross", that it was now operating "south of Rome", across the Mediterranean in Libya.

At the end of the first day of the summit in Washington, on Wednesday, Mr Obama told representatives that "leading up to this summit, there's been a fair amount of debate in the press and among pundits about the words we use to describe and frame this challenge, so I want to be very clear about how I see it.

"Al-Qaeda and ISIL and groups like it are desperate for legitimacy. They try to portray themselves as religious leaders, holy warriors in defence of Islam.

"That's why ISIL presumes to declare itself the Islamic State and they propagate the notion that America, and the West generally, is at war with Islam. That's how they recruit. That's how they try to radicalise young people.

"We must never accept the premise that they put forward, because it is a lie, nor should we grant these terrorists the religious legitimacy that they seek. They are not religious leaders; they're terrorists," he said to a burst of spontaneous applause.

"We are not at war with Islam. We are at war with people who have perverted Islam."

Mr Obama's intent is clear. He seeks to dissuade potential recruits from joining IS by separating it from Islam, and to simultaneously shore up the support of Arab allies in the fight.

But many Americans, conditioned to bold rhetoric in the face of threats, have rejected Mr Obama's carefully calibrated language as weak.

They are infuriated at his refusal to explicitly link terrorism with radical Islam. Mr Obama was ridiculed on Fox News when he called for nations to invest in jobs training and skills to help channel young potential recruits away from terrorism.

And it is true that elements of his speech did not sound well-calibrated to the growing threat. He resorted to his campaign folksiness at one point when he said: "And by the way, the older people here, as wise and respected as you may be, your stuff is often boring compared to what they're doing. You're not connected. And as a consequence, you are not connecting."

This was in reference to the administration's call on the alliance fighting IS to begin to take on the organisation's extraordinary social media machine.

The criticism that followed came not only from Republican and Fox News hawks, but also from some Democrats.

"If you look at some of the conversations that have happened during this summit and the President's speech that we heard just a few minutes ago, I still I think it is a divergent from where we need to be focused," Democratic Congresswoman Tulsi Gabbard said on CNN after the speech.

"If you look at this broad focus on countering violent extremism, which is very hard to define, it's a diversion away from the actual threat coming from this radical Islamic ideology that exists," said Ms Gabbard, a military veteran.

"The administration is misidentifying the enemy and their motivation by saying they are motivated by material aspirations, they are motivated out of poverty or lack of jobs or education or opportunity," she said.

Australia's Attorney-General, George Brandis, will join the proceedings in Washington on Thursday.