WASHINGTON – Sworn allies of the United States across Europe expressed solidarity with an embattled Ukraine at a major summit in Wales on Thursday, where the North Atlantic Treaty Organization has convened to formulate a response to Russia’s military incursion into the country’s east.World leaders expressed agreement on at least one matter upon their arrival: this current NATO summit is the most consequential of its kind since member states gathered to respond to the attacks of September 11, 2001.But just as European diplomats scorned Russia for its actions in the summit’s opening session, US President Barack Obama found himself delayed by meetings on threats posed by Islamic State.Obama met with King Abdullah of Jordan at the summit to synchronize strategies on the growing threat from the group, a terrorist Islamist militia in control of territory across Iraq and Syria, accompanied by US Secretary of State John Kerry, National Security Adviser Susan Rice, and Special Assistant to the President Phil Gordon.The US responded angrily to the beheading of a second American in two weeks on Wednesday, with Obama calling for the destruction of Islamic State and his vice president, Joe Biden, vowing to send its members to the “gates of hell.”British Prime Minister David Cameron arrived in Wales focused on the Islamist group, calling it a direct threat to the UK homeland.“Countries like Britain and America will not be cowed by barbaric killers,” Obama and Cameron wrote together in The Times of London, in an op-ed published with the start of the summit. “We will be more forthright in the defense of our values.”Steven Sotloff, an Israeli-American journalist, was the latest victim used by the group to taunt Western leaders. His beheading was videotaped and shared through social media this week, quickly confirmed as authentic by US and UK intelligence agencies.Foreign Minister Avigdor Liberman said on Thursday that Israel’s government gagged local media from reporting on Sotloff’s citizenship in the interests of his safety.“The censors issued a gag order against reporting that he was an Israeli citizen,” said Liberman. “We are also in close touch with the United States on this entire matter, both ISIS [Islamic State] and the journalist Sotloff.”Sotloff’s killer, a masked man with a London accent, threatened next to kill a Briton should US air strikes against Islamic State assets continue.The US and UK retain the ability to revoke the passports of nationals. Thousands of foreign fighters with European and American passports are currently fighting for Islamic State.“They are the enemy of the United States,” State Department deputy spokeswoman Marie Harf said in a briefing with reporters on Thursday.According to aides in Congress, senior Obama administration officials will brief members of the intelligence committees in the US Senate and House of Representatives this week on the growing threat.Obama also met with the leaders of Germany, France and Italy to discuss both Islamic State and the Russian threat, as well as with Ukrainian President Petro Poroshenko, who attended the Wales summit despite Ukraine not being a member of NATO.Poroshenko hopes that might change, he said during the conference.Obama said he is open to accepting new members to the security alliance, “the strongest in the world,” if aspiring parties offer “meaningful contributions to allied security.”Obama is to host Poroshenko in the Oval Office this month.“President Obama and his European counterparts expressed solidarity with Ukraine, and pledged their continued support for its democracy,” Deputy National Security Adviser Ben Rhodes said from Wales. “The leaders reiterated their condemnation of Russia’s continued flagrant violation of Ukraine’s sovereignty and territorial integrity, and agreed on the need for Russia to face increased costs for its actions.”NATO is expected to announce new sanctions against Russia on Friday, as well as the creation of a rapid reaction force capable of deploying thousands of allied troops to NATO’s east within 48 hours.“We are faced with a dramatically changed security environment.To the east, Russia is attacking Ukraine,” NATO Secretary-General Anders Fogh Rasmussen told reporters on arrival for the NATO summit in a golf resort outside the Welsh city of Newport.The US will also participate in a military exercise with the armed forces of Ukraine in the country’s West, which is “not in response to recent events,” Harf said, while acknowledging the significance of the timing.Reuters contributed to this report.