Pro-Russian insurgents in two of the most tense regions in eastern Ukraine were prepared to conduct a vote Sunday on declaring sovereignty, while the country's acting president warned that it represented "a step into the abyss."
The ballots seek approval for declaring so-called sovereign people's republics in the Donetsk and Luhansk regions, where the insurgents have seized government buildings and clashed with police and Ukrainian troops.
The referendums are not regarded as legitimate by Kiev or the West.
"The United States will not recognize the results of these illegal referenda," State Department spokesperson Jen Psaki said in a statement late Saturday, calling the votes "an attempt to create further division and disorder."
The hastily arranged referendums are similar to the March referendum in Crimea that approved secession from Ukraine. Crimea was formally annexed by Russia days later.