Violence broke out in eastern Ukraine on Sunday days after the truce between Kiev and Moscow. At least three people were killed when a shootout erupted at a checkpoint in a town controlled by pro-Russian separatists. The truce calls for the disarming and withdrawal of armed groups under international supervision. But a top separatist leader has said his forces are not bound by the deal, and little movement has been seen so far. At the White House, National Security Adviser Susan Rice appeared to suggest the United States could target Russia’s oil and gas sector if it is deemed to violate the truce.

National Security Adviser Susan Rice: “There are other potential ways, in the framework of our executive orders, that we could impose costs, should that be necessary, in the event of a dramatic escalation or a significant escalation, including, as we’ve said repeatedly, the potential for Russia to move its own forces on the border inside of Ukraine, that those costs and sanctions could even include targeting very significant sectors of the Russian economy. But beyond that, I’m not going to be specific.”