CARDIFF, Wales — - President Barack Obama and British Prime Minister David Cameron vowed Thursday to confront the Islamic State, saying they “will not be cowed” by the militants who have slain two American journalists and threatened the life of a British captive.The joint statement appeared as an editorial in The Times of London as the two leaders prepared to open a NATO summit that will be dominated by discussions about how to respond to the terrorist threat in Iraq and in Syria, as well as how to counter Russia’s intervention in Ukraine.“If terrorists think we will weaken in the face of their threats they could not be more wrong,” the two wrote. “Countries like Britain and America will not be cowed by barbaric killers. We will be more forthright in the defence of our values, not least because a world of greater freedom is a fundamental part of how we keep our people safe.”They appeared to endorse an enhanced role for NATO in the fight against the extremist group, but offered no details.“By working together we are stronger, whether in standing up to Russia or confronting (the Islamic State),” they wrote, noting that as the NATO alliance meets in Wales, “we must summon up the shared resolve that inspired Nato’s founding fathers. With more than 60 countries represented at the summit, we can build this proud alliance of transatlantic nations into a more effective security network that fosters stability around the world.”The terrorist group must be “squeezed out of existence,” Cameron told SkyNews in an interview.Obama and Cameron arrived together at the summit after visiting a Mount Pleasant Primary School in Newport, Wales, where they talked with children taking part in a NATO-themed lesson. NATO has not received any request from Iraq to fight the Islamic State, but any such request would be "considered seriously," NATO Secretary-General Anders Fogh Rasmussen told reporters outside the summit. He said help could come in the form of military training, as NATO has done before in Iraq.For Obama and Cameron, the summit opened with a meeting on Ukraine with its president Petro Poroshenko, who was expected to brief leaders on potential peace talks with Russian President Vladimir Putin. The talks are scheduled to resume on Friday, but leaders were skeptical about the outcome.“What counts is what is actually happening on the ground and we are still witnessing unfortunately Russian involvement in destabilizing the situation in eastern Ukraine,” Rasmussen said.Ukraine is hoping for greater assistance from NATO, but Rasmussen implied it won’t mean military assistance.Obama and Cameron used the threat of Russia expanding its reach to argue that NATO members need to step up their commitment to NATO, writing that NATO must help Ukraine, and back up its commitment to defend NATO members “with a multinational rapid response force, composed of land, air, maritime and special forces, that could deploy anywhere in the world at very short notice.”That will require more money from NATO members, they said, noting that Britain and the U.S. are two of only 4 alliance members to meet the target of spending 2 per cent of GDP on defence.“Other states must urgently step up their efforts to meet this too,” they wrote, saying it would send “a powerful message to those that threaten us that our collective resolve is as strong as ever.”Analysts say the ask may be difficult, given the stagnant economy of many European nations.