Ukraine's new president-elect promised Monday to negotiate an end to a pro-Russia insurgency in the east and said he was willing to begin talks with Moscow. Yet he described the separatists as "Somali pirates" and authorities in Kyiv launched an airstrike against the militants occupying a major eastern airport.

Russia quickly welcomed Petro Poroshenko's offer for talks, raising hopes that his election will indeed ease the protracted crisis that has fuelled tensions unseen since the end of the Cold War.

But Monday evening, Russia’s foreign ministry called on Kyiv to cease its military operation in Donetsk, and said the Organization for Security and Co-operation in Europe should investigate the clashes.

In a statement, the foreign ministry accused Ukrainian forces of staging "military operations against its own people."

The airstrikes against the separatists in control of Donetsk airport appeared to be the most visible government military operation yet since it started a crackdown on insurgents last month.

In Donetsk, a city of one million, sustained artillery and gunfire was heard from the airport. Fighter jets and military helicopters were seen flying overhead and dense black smoke rose in the air. Many flights to or from Donetsk were delayed or cancelled and access to the airport was blocked by police.

Vladislav Seleznyov, a spokesman for Kyiv's anti-terrorist operation, wrote on his Facebook account that the military had given an ultimatum to the gunmen at the airport to lay down their arms. He said the gunmen didn't comply and the military launched an airstrike.

An Associated Press journalist saw several vehicles full of dozens of heavily armed separatists arrive near the airport. Half an hour later, several flatbed trucks full of reinforcements came in.

Denis Pushilin, a separatist leader in Donetsk, said they had sent their men to the airport after some supporters were detained.

Donetsk media, citing an unnamed health official, said Monday that one person was killed and two others wounded by machine gun fire at the city's main train station. Further details were not immediately available.

'Genuine election'

In Kyiv, international observers hailed Ukraine's presidential vote as a "genuine election," saying it was held freely and fairly Sunday.

About 500 Canadian election observers, including former Ontario premier Mike Harris and Conservative Senator Raynell Andreychuk, concluded that the "election is a genuine reflection of the will of the people of Ukraine" despite the violence in the east.

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A pro-Russian armed militant is shown in eastern Ukraine on Monday. (Alexander Zemlianichenko/Associated Press)

"I think these elections demonstrated a clear commitment to building a better future free form Russian-sponsored diversion and violence," said Foreign Affairs Minister John Baird. "Canada was proud to have contributed hundreds of observers to monitor and report on the conduct of these elections. We'll be issuing a report as soon as possible."

Candy magnate Poroshenko, known for his pragmatism, supports building strong ties with Europe but also has stressed the importance of mending relations with Moscow. Upon claiming victory, he said his first step as president would be to visit the Donbass eastern industrial region, where pro-Russia separatists have seized government buildings, declared independence and battled government troops in weeks of fighting.

"Peace in the country and peace in the east is my main priority," Poroshenko said Monday, signalling that he would end the Ukrainian army's much-criticized campaign to drive out the separatists.

"The anti-terrorist operation cannot and should not last two or three months," he said. "It should and will last hours."

The president-elect also had harsh words for the pro-Russia gunmen, comparing them to Somali pirates.

"Their goal is to turn Donbass into a Somalia, where they would rule with the power of machine guns. l will never allow that to happen on the territory of Ukraine," Poroshenko said, adding that he hoped Russia would support his efforts to stabilize the east.

Local journalists applaud new PM

CBC correspondent Nahlah Ayed said from Kyiv that Poroshenko became emotional as he spoke and elicited applause from some of the local journalists.

Poroshenko said he would go after gunmen "anywhere." Ayed said that was a reference not just to pro-Russian militia in the east, but armed men walking around central Kyiv since the revolution.

Poroshenko's spokesman told The Associated Press that the date for his inauguration has not been set yet.

Ukraine election Petro Poroshenko

Billionaire Petro Poroshenko claimed Ukraine's presidency after exit polls gave him an absolute majority in a first round of voting. (Stringer/Reuters)

In Moscow, Foreign Minister Sergey Lavrov said Russia appreciated Poroshenko's statements about the importance of Ukraine's ties with Russia and his pledge to negotiate an end to fighting in the east.

"We are ready for dialogue with representatives of Kyiv, with Petro Poroshenko," Lavrov said at a briefing, adding it was a chance that "cannot be wasted." He emphasized that Moscow saw no need for any involvement by the United States or the European Union in those talks.

"We don't need any mediators," he said pointedly.

Lavrov also noted Russia's longstanding call for the Kyiv government to end its military operation in eastern Ukraine.

Less than 20 per cent of the polling stations in eastern Ukraine were open Sunday after gunmen intimidated residents by smashing ballot boxes, shutting down polling centres and issuing threats. But nationwide, about 60 per cent of Ukraine's 35.5 million eligible voters turned out, and long lines snaked around polling stations in the pro-Western capital of Kyiv.

Intimidation and abduction

Joao Soares, special coordinator for the OSCE observer mission in Kyiv, hailed Sunday's vote even as he said monitors saw multiple threats, intimidation and abduction of election officials in the east.

"Ukrainian authorities should be commended for their efforts in the extraordinary circumstances to facilitate an election" which was held in parts of Ukraine's volatile east, Soares said.

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Canada's election observers said the Ukrainian presidential election reflected the will of the voters. (Nahlah Ayed/CBC)

With votes from 80 per cent of the precincts counted Monday, Poroshenko was leading with about 54 per cent of the vote in the field of 21 candidates. Former Prime Minister Yulia Tymoshenko was running a distant second with 13 per cent. Election officials confirmed that Poroshenko had avoided a runoff.

Poroshenko struck a tone of unity Monday, saying he had no "rivals or political opponents in the race" and all of the other main candidates had congratulated him.

"More than ever, Ukraine now needs to be united," he said.

The election, which came three months after pro-Moscow President Viktor Yanukovych was chased from office following months of street protests, was seen as a critical step toward resolving Ukraine's protracted crisis.

Since Yanukovych fled in February, Russia has annexed Ukraine's southern Crimea Peninsula, the eastern regions of Luhansk and Donetsk have declared independence, and the interim Ukrainian government has launched an offensive to quash an uprising.

The interim Kyiv government and the West have accused Russia of backing the separatist uprising. Moscow has denied the accusations.

U.S. President Barack Obama praised Ukrainians for participating in the voting "despite provocations and violence." He said the U.S. supports Ukraine's sovereignty and territorial integrity and is eager to work with the next president.

With files from CBC News and Reuters