US Secretary of State John Kerry says the global coalition fighting Islamic State must "relentlessly" pursue them so they have nowhere to run or hide.
Speaking in Rome at the start of a meeting of the Small Group of the Global Coalition to Combat ISIL/Daesh, Kerry said the coalition created in mid-2015 now comprises 66 nations and remains committed to destroying the terror group.
Kerry hugged and chatted with Australian Foreign Minister Julie Bishop before the start of Tuesday's meeting.
Australia has about 780 defence personnel deployed in the Middle East engaged in Operation Okra to counter IS in the region. RAAF fighter jets have carried out air strikes on IS targets in Syria and Iraq.
Kerry told the delegates that much progress had been made since the creation of the coalition, including the recapture of the city Ramadi by Iraqi forces and 10,000 air strikes that had killed about 90 senior IS leaders and hammered their heavy weapons, training camps and oil fields.
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"Our concentrated effort is moving in the right direction," he said.
"We are surely not here to brag about anything, we are here to recommit, to re-evaluate.
"But eight months later it is fair to say our commitments is making a difference."
Kerry said it was also necessary to pay attention to the situation in Libya, where IS had a foothold, and to ensure sufficient international funding for rebuilding in reconquered cities in Iraq.
He said Daesh was "like a weed" that could have its top pulled off but continue to grow.
"This battle is ultimately going to be won by forces on the ground," Kerry said.
He said the coalition would push ahead with strategies that had been proven to work and it would do so relentlessly, "so Daesh has no place to run, no place to hide".
"I am absolutely confident, I have no doubt, we are going to degrade and destroy Daesh."
The meeting's co-chair, Italian Foreign Minister Paolo Gentiloni, said the coalition should not underestimate Daesh, adding that a dangerous new phase may be starting.
He said the more Daesh was squeezed in its core territory the more it was likely to carry out terror attacks "in our own countries".
Heavy security is in place in central Rome, with armoured cars, soldiers with sub-machine guns and many police on guard at key government venues and tourist sites.
The Rome meeting comes as a peace conference continues in Geneva, with UN-led negotiators meeting separately with representatives of the Syrian regime and opposition groups in a bid to achieve a ceasefire and steps towards a political settlement.
