Ukraine is threatening to send troops into eastern towns today after a deadline passed for pro-Russian demonstrators to stand down. The protesters have occupied state buildings in a call for breaking off from Ukraine and joining Russia. Ukraine has warned of a full-scale assault to retake the buildings and end the standoff. At the United Nations, U.S. Ambassador Samantha Power accused Russia of orchestrating the unrest.

Samantha Power: “These armed units, some wearing black and orange St. George’s ribbons associated with Russian Victory Day celebrations, raised Russian and separatist flags over seized buildings and have called for referendums and union with Russia. We know who is behind this. Indeed the only entity in the area capable of these coordinated professional military actions is Russia.”

A Ukrainian operation could spark a new military incursion by Russia, which has massed tens of thousands of troops on its Ukraine border.