"We would welcome an indication from Russia that they would accept the results of a free and fair and democratic election in Ukraine," said White House spokesman Jay Carney.
Carney's cautious language and choice of tense however indicated US skepticism over Putin's comments, after Washington has spent weeks condemning what it sees as Russia's deliberate destabilisation of Ukraine.
"Right now we are focused on Ukraine's efforts to carry out that election freely and fairly," Carney told reporters aboard Air Force One.
Putin, who has in the past given only grudging backing to the election, appeared to suggest he would accept the outcome of the vote.
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"We understand that the people of Ukraine want their country to emerge from this crisis. We will treat their choice with respect," Putin said at an economic forum in Saint Petersburg.
Sunday's vote is seen as the most crucial since Ukraine's independence in 1991, with the country facing the threat of partition and teetering on the brink of economic collapse.