(AP) - The United States began building a case Friday linking pro-Russian separatists to the shocking downing of a passenger jet in Ukraine. A somber President Barack Obama declared the deaths of those on board, including at least one American, an "outrage of unspeakable proportions."



Obama said the U.S. believes the Malaysia Airlines plane was felled by a surface-to-air missile launched from an area near the Ukraine-Russia border that is controlled by Kremlin-backed separatists. Even as he cautioned that the exact circumstances were still being determined, the president turned his sights on Russia, saying the insurgents would not be capable of carrying out such an attack without Moscow's support.



"We know that they are heavily armed and they are trained, and we know that that's not an accident," Obama said. "That is happening because of Russian support."



The president spoke shortly after Samantha Power, the U.S. ambassador to the United Nations, outlined preliminary evidence against Russia and the separatists during an emergency meeting of the U.N. Security Council. Power said separatists were spotted Thursday with an SA-11 anti-aircraft missile at a location close to the site where the plane came down and that they had boasted on social media sites about shooting down a plane, then later deleted those posts.



Power joined Obama in calling for an immediate international investigation, and she warned that the separatists and those supporting them would have "good reason to cover up evidence of their crime." The U.S. has called for evidence from the crash site to remain in Ukraine until investigators determine who is responsible.



The American killed in the incident was identified as Quinn Lucas Schansman. Officials said they were still working to confirm whether any other U.S. citizens were on board the plane.



For Obama, the downed plane adds new complexity to U.S. efforts to quell the months-long conflict between Russia and Ukraine. Increasingly stringent economic sanctions imposed by the U.S. and Europe, including a new round of penalties announced a day before the plane was shot down, have done little to change Russian President Vladimir Putin's approach.



Obama warned Russia anew on Friday that the U.S. has the capacity to increase the economic pain, but he outlined no specific potential actions. He did say he saw no U.S. military role in the conflict that has stemmed in part from Russia's annexation of the Crimean Peninsula from Ukraine.



All 298 people aboard the Malaysian plane were killed in Thursday's incident. The victims included vacationers, students and a large contingent of scientists. The passengers came from a dozen countries, spreading the impact of the Ukraine crisis around the globe.



"This certainly will be a wake-up call for Europe and the world that there are consequences to an escalating conflict in eastern Ukraine - that it is not going to be localized, it is not going to be contained," Obama said.



The president has spoken with several world leaders since the crash, including Ukrainian President Petro Poroshenko, Malaysian Prime Minister Najib Razak, and Prime Minister Mark Rutte of the Netherlands. The flight originated in Amsterdam and nearly 200 of those killed were Dutch.



Obama also spoke with Russia's Putin just as initial reports of the crash were coming in. On Friday, the president stopped short of blaming Putin for the downing of the plane, but he said the Russian leader could bring the broader conflict to an end.



"He has the most control over that situation, and so far at least he has not exercised it," the president said.



A U.S. official said all available evidence, including satellite imagery, pointed to the plane being shot down with an SA-11 anti-aircraft missile fired by pro-Russian separatist forces. The official said the U.S. detected three separate events associated with the shootdown: the launching of the missile from the Ukraine side of the border, the missile's impact with the plane and the plane slamming into the ground.



That official was not authorized to discuss U.S. intelligence matters publicly by name and commented only on condition of anonymity.



Power, during her remarks at the United Nations, said Ukrainian forces as well as the separatists have SA-11 systems in their inventory. However, she said the U.S. was not aware of those systems being in the area of the shooting, and she noted that Ukrainian air defenses have not fired any missiles during the dispute with Russia.



The State Department said the FBI and National Transportation Security Board were each sending at least one agent to Ukraine, and perhaps more later, to assist with the crash investigation.



A command center has been set up at the State Department, where officials from agencies participating in the delegation gathered Friday morning for a briefing from the CIA on the political and military situation.