The U.S. ambassador to the United Nations blamed Russia for creating unstable conditions that allowed an advanced missile to take down a Malaysian passenger plane over Ukraine, and possibly for providing the technical expertise needed to fire the missile to Russian separatists.

“The context for yesterday’s horror is clear,” U.S. Ambassador to the UN Samantha Power said at a UN Security Council meeting Friday morning. “Separatist forces backed by the Russian government continue to destabilize Ukraine, and undermine the efforts of Ukraine’s elected leaders to build a democratic Ukraine that is stable, unified, secure, and able to determine its own future.”

Russia Ukraine United Nations Samantha Power Vladimir Putin

United States U.N. Ambassador Samantha Power speaks during a U.N. Security Council meeting at United Nations headquarters, Friday, July 18, 2014. (AP Photo/John Minchillo)

Power called out Russian President Vladimir Putin in particular for continuing to send troops and materiel to Ukraine and neighboring areas, despite Putin’s pledge to seek peace in the region.

“Russia says that it seeks peace in Ukraine, but we have repeatedly provided this council with evidence of Russia’s continued support to the separatists,” she said. “Time after time, President Putin has committed to work toward dialogue and peace — in Geneva in April, in Normandy in June, and in Berlin earlier this month — and every single time, he has broken that commitment.

“Most Council members and most members of the international community have been warning for months about the devastation would come if Russia did not stop what it started, if it did not rein in what it unleashed.”

Power said that while information is still being gathered about the missile that took down Malaysian Airlines flight MH17, she said the U.S. cannot rule out that Russia provided a heavy-duty surface-to-air missile system to Russian-backed separatists.

“Because of the technical complexity of the SA-11, it is unlikely that the separatists could effectively operate the system without assistance from knowledgeable personnel,” she said. “Thus, we cannot rule out technical assistance from Russian personnel in operating the systems.”

She also said Russian separatists have show down other planes and helicopters over the last several weeks, and said the shooting down of the Malaysian passenger plan “follows a pattern.”

“If indeed Russian-backed separatists were behind this attack on a civilian airliner, they and their backers would have good reason to cover up evidence of their crime,” she said.

Power said Russia’s failure to help control the situation in Ukraine is what has led the U.S. and other countries to impose sanctions against Russia. But at the same time, she called on Russia to help the international community secure the area so a full investigation of the downed plane can take place.

Among other things, Power said a full cease-fire is needed to allow investigators to examine the remains of the plane. “Russia needs to help make this happen,” she said.

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