Russia has vetoed a UN Security Council draft resolution that declared a planned referendum on the status of Ukraine's Crimea region "can have no validity" and urged nations and international organizations not to recognize it.
The Russian veto of the draft resolution, drawn up by the United States, was expected.
Moscow, which has sent military forces to the Crimea, is backing Sunday's referendum, which would transfer control of the region from Ukraine to Russia.
The brief resolution noted that the referendum was not backed by the Ukrainian government in Kiev.
"This referendum can have no validity, and cannot form the basis for any alteration of the status of Crimea," it states. It calls on "all states, international organizations and specialized agencies not to recognize any alteration of the status of Crimea on the basis of this referendum."
John Kerry warned of "consequences" after his Russian counterpart made clear Moscow would respect the outcome of Crimea's referendum.
Foreign ministers meeting in Brussels will decide on Monday on sanctions for Russia if there is no de-escalation in Ukraine.
Crimea's new information minister has told ITV News that the planned referendum is no different to the situation in Scotland and Catalonia.