Russia has urged the Kiev government to stop a 'military operation against its own people' and called for the Organisation for Security and Cooperation in Europe to investigate clashes with pro-Russian separatists in the eastern city of Donetsk.
At least one person has been killed and two injured during an assault on Donetsk airport, local authorities have said.
There was no full account from either side of casualties. But the press service of the regional administration said one man had been killed and two injured from shrapnel of a shell which struck a part of the railway station serving the airport.
Ukraine's military has launched an operation against rebels who have taken over the international airport in Donetsk, a security official has said.
A statement said paratroopers had landed at the airport following a strike by Ukrainian aircraft earlier.
The rebel gunmen are reported to have stormed the airport this morning in what may be a show of defiance following the Ukrainian presidential elections, which look likely to see victory for businessman Petro Poroshenko.
Shots have been fired around Donetsk international airport in eastern Ukraine with smoke billowing from the airport area, an eyewitness told Reuters.
Ukraine's next president, Petro Poroshenko, says he hopes to meet Russia's leaders in the first half of June and said restoring stability in eastern regions of his country would require Moscow's involvement.
Armed pro-Russian separatists have taken control of some towns and cities in mainly Russian-speaking eastern Ukraine and they prevented many people in the region from taking part in Sunday's presidential election which exit polls show Poroshenko to have won.
"I hope Russia will support efforts to tackle the situation in the east (of Ukraine)," Poroshenko told a news conference.
He repeated his readiness to speak with separatists who laid down their weapons but added he would not meet "terrorists" who threatened the security of the state.
Russia says it is ready for dialogue with Petro Poroshenko, who is on course to become Ukraine's president, but warned the Kiev authorities not to step up armed operations against separatists in the east.
Echoing remarks by President Vladimir Putin in the past few days, Foreign Minister Sergei Lavrov said genuine dialogue between Kiev and the east - where pro-Russian separatists have rebelled against the national leadership - was the key to resolving Ukraine's crisis.
Ukraine's presidential election is a "decisive signal of their support for reform", William Hague declared as he praised voters for defying disruption by pro-Russian separatists.
The Foreign Secretary said every vote cast was "an individual act of courage" as he pledged to work with the country's new leader on ambitious reforms.
Exit polls suggested a convincing win for billionaire chocolate tycoon Petro Poroshenko, who is said to have received 55.9% - with former prime minister Yulia Tymoshenko a distant second.
Voting was severely disrupted in parts of the east of the country, where separatists have seized control amid fighting that has claimed at least 20 lives in recent days.
Ukraine's Petro Poroshenko, set to be the new president after today's election, said he would never recognise Russia's "occupation of Crimea" and ruled out negotiating with separatists.
Asked about relations with Russia, he said the "sovereignty and territorial integrity" of Ukraine were paramount for him.
The confectionery tycoon also ruled out negotiations with pro-Russian separatists in the east of the country until they put down their weapons.
Businessman Petro Poroshenko has won an outright first round victory in Ukraine's presidential election with 55.9 percent of the vote, exit polls have indicated.
The confectionery magnate, who is known as the "Chocolate King", was well ahead of former prime minister Yulia Tymoshenko in second place with 12.9 percent in the poll.
An Italian journalist and his Russian translator have been killed in fighting between pro-Russia forces and Ukrainian government troops in eastern Ukraine, the Italian Foreign Ministry said today.
The bodies of Andrea Rocchelli, a freelance photographer who worked with the Cesura photographers' collective, and his colleague, Andrey Mironov, were taken to a hospital in the town of Slaviansk.
French freelance journalist William Roguelon, who had been travelling with the two men, said
the group came under fire on the outskirts of the eastern town on Saturday afternoon.
He said Rocchelli and Mironov were hit by mortar fire between rebels and Ukrainian troops while he had walked off looking for help.