Pro-Moscow separatists in eastern Ukraine ignored a public call by Russian President Vladimir Putin to postpone a referendum on self-rule, declaring they would go ahead on Sunday with a vote that could lead to war.
The decision, which contradicted the conciliatory tone set by Putin just a day earlier, caused consternation in the West, which fears the referendum will tear Ukraine apart.
U.S. Deputy Secretary of State William Burns said Russia was heading down a "dangerous and irresponsible path" and the situation in Ukraine was "extremely combustible."