Ukraine handed chocolate tycoon Petro Poro­shenko a commanding victory in its presidential election Sunday, giving the pro-European billionaire a chance to resolve a conflict that has created the greatest tensions between the West and Russia since the Cold War.

The new leader takes the office once held by pro-Kremlin Viktor Yanukovych, who was ousted in February after anti-government protests. That revolt led to Russia’s annexation of the Crimean Peninsula, the rise of a separatist movement in Ukraine’s east and a torrent of violence that increasingly looks like a low-grade civil war. All are massive challenges that will test a longtime politician who has promised to navigate between Russia and the West.

Poroshenko immediately moved Sunday to paint himself as a conciliator, declaring that his first official act after inauguration would be to visit the heart of the separatist rebellion in the Donets Basin.

“The first steps of our entire team at the beginning of the presidency will concentrate on ending the war, ending the chaos, ending the disorder and bringing peace to Ukrainian soil, to a united, single Ukraine,” he said at a victory rally Sunday. “Our decisive actions will bring this result fairly quickly.”

He has also said he wants to lead Ukraine to closer ties with the European Union.

But with violence preventing many citizens in pro-Russian eastern Ukraine from voting, it remained far from clear how much people there would accept Poroshenko’s mandate. Separatists in the region had vowed to disrupt the vote, and they largely succeeded Sunday, with many polling stations shuttered, ballots stolen, and election officials threatened and even kidnapped. Citizens in eastern Ukraine have long been skeptical of centralized power in Kiev, and many voted May 11 in a separatist-organized referendum in favor of autonomy.

Russian President Vladimir Putin said a day before Ukraine voted that Russia would “cooperate with the authorities that will come to power as a result of the election,” but he added that he continued to consider Yanukovich the legitimate president of the country.

Exit polls released immediately after balloting ended showed Poroshenko taking more than 55 percent of the vote, avoiding a runoff that would have left Ukraine without an elected leader for three more weeks. His closest rival, former prime minister Yulia Tymoshenko, whom polls indicated garnered 12 to 13 percent, conceded. Official results will be announced Monday.

Two far-right nationalist candidates appeared to do poorly. Oleg Tyagnibok of the Svoboda party and Dmitry Yarosh of the Right Sector party each received roughly 1 percent of the vote, according to the exit polls.

The Central Election Commission estimated final voter turnout nationwide at 60 percent, a spokesman said. Turnout in the 2010 election — in which residents of eastern Ukraine and Crimea could vote freely — was 67 percent. A regional breakdown of the final turnout figures was not immediately available, but 14 percent of the country’s registered voters live in the two eastern regions were voting was impeded Sunday.

Poroshenko, 48, is a soft-spoken businessman who built a candy empire out of the ashes of Ukraine’s post-Soviet economy. Forbes estimates his wealth at $1.3 billion. He has worked on both sides of the country’s political divide, as foreign minister during the pro-Western presidency of Viktor Yushchenko and briefly as economy minister under Yanu­kovych. But Poroshenko allied himself with protesters shortly after Yanukovych rejected a deal in November to move toward integration with the European Union.

Many of the anti-corruption civil society groups that occupied Kiev’s Independence Square in opposition to Yanukovich fear that the country’s new president could be an old-style representative of rule by Ukraine’s wealthiest.

Poroshenko said Sunday that he wants to hold new parliamentary elections this year, a move that would pave the way for a full revamp of the government. Yanu­kovich’s pro-Russian Party of Regions still holds a plurality of seats in the legislature.

Problems beyond the capital

In Kiev on Sunday, voters stood in long lines as they waited to fill out the large paper ballots for president. Many said they were choosing Poroshenko as a conciliatory figure.

Poroshenko “is the one person who is actually neutral,” said Alexander Stelmakh, 36, a construction worker who came with his 3-year-old son to vote at School No. 15 in the leafy Holoseevsky neighborhood on the outskirts of the city.

But in Ukraine’s troubled east, problems with voting were widespread, and pro-Russian separatists attacked polling places, according to the office of Donetsk’s governor, Serhiy Taruta. Only 426 polling stations out of 2,430 were open in the region, and none in the city of Donetsk, which has 1 million residents, the Donetsk Regional Administration said.

There were difficulties even in areas nominally under government control. Sunday morning, people started trickling into a polling station in Veliko Novoselovka, a town where Ukrainian troops backed by armored personnel carriers operated a roadblock along the highway leading to Donetsk, 60 miles east. A second roadblock was just outside town.

But voters were initially turned away because of a lack of ballots. The district’s top election official had been abducted Saturday and the ballots stolen, said the election official in charge of the polling station, who would give his name only as Oleksandr. By mid-afternoon, ballots arrived under army escort. But officials were still numbering and affixing official stamps to them more than three hours later, and no one in town had been able to vote.

“We very much wanted to vote. We want to end this disorder,” said one woman, a retired schoolteacher with tears in her eyes who gave only her first name, Tatyana.

In Krasnoarmiisk, a town 30 miles northwest of Donetsk, voting proceeded normally at School No. 9, but with only about 10 percent turnout, Natalyia Tyrhaninova, the head of the district election commission, said late Sunday.

Violence continues

The latest violence Sunday was a reminder of the challenges facing Ukraine’s new leader. One man was killed and another wounded in a skirmish near the town of Novoaidar, Deputy Interior Minister Serhiy Yarovoi told reporters, without giving details. Interfax reported that the victims were separatists. In Mariupol, a special police unit apprehended top separatist leader Denis Kuzmenko and killed one of his bodyguards, the Ministry of Internal Affairs said in a statement.

Also Sunday, the deaths of Italian photojournalist Andrea Rocchelli, 30, and his Russian interpreter, Andrei Mironov, 60, were confirmed by the Organization for Security and Cooperation in Europe. The group said the two were killed the previous day by mortar fire near the rebel-held city of Slovyansk, but the exact circumstances remain unclear. Mironov, a former dissident who was imprisoned during the waning years of the Soviet Union, was a longtime fixture in Moscow’s journalism community and worked for many Western news outlets there, including The Washington Post.

Kunkle reported from Donetsk. Abigail Hauslohner in Moscow, Daniela Deane in London, and Anastasiia Fedosov and Aleksey Ryabchyn in Donetsk contributed to this report.