Meeting in Rome, ministers from the 23 countries involved in the US-led coalition battling the extremist group said progress was being made in pushing IS back in Syria and Iraq and cutting off its sources of finance and energy.
And they pledged to step up their action.
"We will intensify and accelerate the campaign against ISIL/Daesh in Iraq and Syria, act in concert to curb its global ambitions, and take every measure to ensure the protection of our citizens," they said in a statement.
"We reaffirm our commitment to deliver a lasting defeat to this barbaric organisation."
The statement expressed concern over "the growing influence" of IS in Libya but stopped short of threatening air strikes. It said only that the allies would "continue to monitor closely developments there, and stand ready to support" a proposed national unity government that is struggling to establish itself.
Italian Foreign Minister Paolo Gentiloni and US Secretary of State John Kerry opened the talks by telling their allies that IS was adapting to the pressure on its heartland and redirecting its efforts towards Libya and into attacks like those in Paris, Ankara and San Bernadino, California.
"We are surely not here to brag about anything," Kerry cautioned after saying IS fighters have lost 40 percent of their territory in Iraq and 20 percent in Syria.
Gentiloni added: "If anything we need to be ever more wary and more watchful because we know that the more Daesh is squeezed in its core territories, the more tempted it is to pursue its terrorist activities elsewhere.
"We are witnessing renewed activity in Libya and in sub-Saharan Africa," he said.
Within the coalition, Italy has taken the lead in planning how to address the IS threat which is just a short boat ride from its southern shores, in and around the Libyan coastal city of Sirte.
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NO MILITARY INTERVENTION
But Rome's focus is firmly on trying to rally the international community behind efforts to get a national unity government established and helping it stabilise a country that descended into chaos after the ouster of Moamer Kadhafi in 2011.
Direct military intervention against IS fighters is not on the immediate agenda, French Foreign Minister Laurent Fabius told reporters, rubbishing reports that Paris was pushing for strikes.
"There is absolutely no question of military intervention in Libya," Fabius said. "There is pressure (for that) but that is not the position of the government."
Gentiloni also played down the need for "hasty military intervention."
Washington says it has built a 66-nation coalition to fight the IS group, with Afghanistan becoming the latest country to join, Kerry said.
But a so-called "small group" of 23 nations has taken the lead in carrying out air strikes in Iraq and Syria and training and arming local forces to fight the jihadists.
Kerry said the effort now needs to be stepped up, citing the example of Washington's deployment of small numbers of special forces troops inside Syria.
The allies need to "push ahead with a strategy we have learned will work and to do so relentlessly, giving Daesh no time to regroup, no place to run, no safe havens in which to hide," he said.
Fabius said France also supported intensified strikes in Syria but suggested "more strategic" targeting was required while peace talks are under way in Switzerland.
"We cannot bomb in Syria and negotiate in Geneva," he said in an explicit allusion to Russia's air campaign in Syria.