KIEV, May 21 – Petro Poroshenko, the frontrunner in Ukraine's presidential election, appealed to voters on Wednesday to hand him victory outright in Sunday's first round of voting or face a risk of "destabilization" that might prevent a second-round runoff, Reuters reported.

Opinion polls make Poroshenko, a confectionery magnate, the runaway favorite to win the election, which Kiev's interim leaders say is vital to restore stability in a country facing Russian hostility and a separatist revolt in its eastern region.

Billed as Ukraine's most important election since it became independent of Moscow in 1991, it was called after street protests toppled Kremlin-backed Viktor Yanukovych in February. He fled to Russia, which then seized Ukraine's Crimea and inspired separatist revolts in Russian-speaking eastern towns.

Poroshenko, 48, known as the "chocolate king" because of his business interests, could win more than the 50 percent of votes needed on Sunday to win outright and avoid a second round on June 15 - a scenario he said would be best for stability.

"Today let us be realistic: if the election is not over in the first round, the second round might not take place. The level of destabilization might be such that we will have to fight for legitimacy," he said during a visit to the Black Sea port of Odessa, according to Interfax news agency.

Poroshenko appeared to be suggesting that further pressure from Russia, which has had tens of thousands of troops massed near the border with Ukraine, or a surge in action by the pro-Russia separatists who control key towns and buildings in the east, could derail the election.

Russian President Vladimir Putin, who has condemned the overthrow of Yanukovych as a coup, continued to cast doubt on the legitimacy of Ukraine's election on Wednesday. He said during a state visit to China that it would be more logical for Kiev to hold the vote after a referendum on a new constitution.

"It will be very hard for us to build relations with people who come to power against the backdrop of a continuing punitive operation in southern and southeastern Ukraine," Putin said, referring to anti-separatist military operations by Kiev's forces.

Former prime minister Yulia Tymoshenko, a dominant figure in Ukrainian politics for over a decade but whose star has faded amid the turmoil and after a jail sentence, trails well behind Poroshenko in second place in the opinion polls.

With emotions still high after months of upheaval in which dozens of anti-Yanukovych protesters were shot dead by police, Ukraine looks set to record one of its biggest election turnouts ever, despite the loss of Crimea and the separatists' determination to prevent voting in the towns they hold.

The Committee for Voters of Ukraine, a watchdog body, expected a turnout of at least 70 percent and possibly as high as 80 percent - which would be significantly more than the 69 percent registered in the run-off vote in 2010 which brought Yanukovych to power at the expense of Tymoshenko.

"Today 60 percent of Ukrainians declare that they will definitely vote and approximately 20 percent more say that they are likely to take part ... We predict no less than 70 percent of citizens will take part," said Oleksandr Chernenko, president of the Committee for Voters of Ukraine.

Turnout was expected to be particularly high in the capital and in the nationalist-minded western regions, he added.

Election officials in the eastern industrial hub of Donetsk, where separatists have declared an independent "people's republic", said this week that harassment and intimidation had forced them to close down the five electoral commission bodies in the city of one million.

However, some residents of Donetsk and of nearby Luhansk are expected to travel outside their regions to cast their ballot on Sunday. The two regions have a combined electorate of 5.1 million in a country with a total voter base of 35.5 million. (rt/ez)