Samantha Power UN MH17
U.S. Ambassador to the United Nations Samantha Power addresses the U.N. Security Council at the U.N. headquarters in New York July 18, 2014. REUTERS/Lucas Jackson

Samantha Power, U.S. ambassador to the United Nations, said Friday that if Russia-backed separatists were found responsible for shooting down Malaysia Airlines Flight MH17, investigators “cannot rule out technical assistance from Russian personnel in operating the system” that downed the plane.

Power’s remarks, made during an emergency meeting of the United Nations Security Council in New York, were the strongest implication from a U.S. official so far that Russia may have been involved in Thursday’s plane crash in Ukraine near the Russian border, which left 298 dead.

The ambassador acknowledged that flight MH17 was likely shot down from a surface-to-air missile over a separatist-held region in eastern Ukraine. But if pro-Russia separatists were indeed responsible for taking down the plane, she said, Russia’s possible role must not be ignored in the investigation. The “technical complexity” of the weaponry used would make it unlikely that the rebels operated without some assistance from military personnel, Power said.

Power also called on Russia to calm tensions in eastern Ukraine. “This tragedy only underscores the determination in which we insist Russia immediately take concrete steps to de-escalate the situation in Ukraine,” she said.

“This war can be ended,” Power added. “Russia must end this war.”