The United States will not recognise weekend elections planned by pro-Kremlin rebels in eastern Ukraine, even while hailing a breakthrough energy deal between Kiev and Moscow.
France, Germany, the European Union and the transatlantic NATO alliance have also condemned Sunday's leadership vote in Ukraine's Donetsk and Luhansk regions.
"We deplore the intent of separatists in parts of eastern Ukraine to hold illegitimate so-called local 'elections' on Sunday," White House National Security Council spokeswoman Bernadette Meehan said in a statement.
"If held, these `elections' would contravene Ukraine's constitution and laws and the September 5 Minsk Protocol."
The United States has said it would, however, recognise a December 7 vote planned in the region and backed by the international community.
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In a four-way call earlier, the leaders of Ukraine, Germany and France urged Russian President Vladimir Putin not to recognise the polls.
Moscow has already welcomed the polls but Ukrainian President Petro Poroshenko said they would hurt the shaky peace process in the six-and-a-half month conflict that has killed more than 3700 people.
"The United States will not recognise any results announced from this so-called election, and we call on all members of the international community to do the same," Meehan said.
She cautioned Russia against using such a vote "as a pretext to insert additional troops and military equipment into Ukraine".
At the State Department, spokeswoman Jen Psaki also warned that the United States was still concerned about the "illegitimate and illegal" weekend elections.
Kiev reached a breakthrough deal with Moscow late Thursday brokered by the European Union in Brussels to resolve their long conflict over energy supplies.
In the agreement published by Ukraine's government, Kiev must pay the first $US1.45 billion ($A1.57 billion) tranche of its debt before any gas deliveries are resumed and the full amount of $US3.1 billion ($A3.35 billion) by the end of the year in order to receive gas in 2015.
"The agreement is a positive step," Psaki said.
