Ukrainian President Petro Poroshenko casts his ballot in a polling station in Kiev on October 26, 2014.
US President Barack Obama on Monday hailed "successful" Ukrainian elections that saw pro-Westerners score a big win in parliament, and blasted Russia for preventing voters in the east from casting their ballots.
Politicians were hard at work to build a ruling coalition, with initial results showing Prime Minister Arseniy Yatsenyuk's People's Front and the Petro Poroshenko Bloc neck and neck with about 22 percent of votes each.
"On behalf of the American people, I congratulate the people of Ukraine on holding successful parliamentary elections on October 26," Obama said in a statement.
"Yesterday's parliamentary vote represents another important milestone in Ukraine's democratic development. We look forward to the convening of the new parliament and the quick formation of a strong, inclusive government."
Observers from the pan-European Organization for Security and Cooperation in Europe (OSCE) said the election, held in challenging conditions, "largely upheld democratic commitments."
But in a fiery reminder of the hurdles Poroshenko faces, an election-period lull in the rebel-held east ended early Monday in a barrage of artillery fire.
Critical of alleged Russian obstructionism in the restive east, Obama called on Moscow to ensure its "proxies" in parts of Donetsk and Luhansk would allow voters to cast their ballots in December 7 local elections.
"It is clear that Russian authorities occupying Crimea and Russian-backed separatists in parts of eastern Ukraine prevented many Ukrainian citizens from exercising their democratic rights to participate in national elections and cast their votes," he said.
"The United States will not recognize any election held in separatist-held areas that does not comport with Ukrainian law and is not held with the express consent and under the authority of the Ukrainian government."
Obama vowed to support Ukraine's efforts to peacefully resolve the conflict in the east and the return of the Crimean Peninsula, which Russian troops annexed in March.
Moscow says it is simply coming to the aid of Russian speakers who feel threatened by Ukraine's lurch toward the West.
In response, the United States and European Union have imposed damaging economic sanctions on Moscow, fueling the kind of East-West tensions last seen in the Cold War.