Coalition talks intensify Tuesday between the pro-Western winners of Ukraine's parliamentary poll, while attacks by pro-Russian insurgents in the east highlight the obstacles to their promises of peace and deeper EU ties.

The day after pro-West and moderate nationalist forces backing President Petro Poroshenko scored a big win in Sunday's election, the hard work of forming a ruling coalition began.

With 67 percent of precincts reporting, Prime Minister Arseniy Yatsenyuk's People's Front and the Petro Poroshenko Bloc were neck and neck, winning about 22 percent of the votes each.

Expectations were that the two will work together in government, with Yatsenyuk retaining the premier's post.

However, the pro-West regime now faces giant challenges: restoring relations with Russia, ending the insurgency, eradicating corruption, tackling massive debt, and resolving a near permanent crisis over Russian gas supplies.

Russia welcomed the outcome of the election as backing for "a peaceful resolution" of the separatist war being waged by pro-Moscow rebels in eastern Ukraine.

Deputy Foreign Minister Grigoriy Karasin said the election was valid "in spite of a rather harsh and dirty campaign".

Western leaders hailed the general election as a democratic milestone.

The head of the EU executive, Jose Manuel Barroso, called the vote a "victory of democracy and European reforms".

France said the results "confirmed the people's fundamental choice".

US President Barack Obama called the election -- declared mostly fair by a European observer team -- an "important milestone in Ukraine's democratic development".

His Vice President Joe Biden will visit Ukraine, and Turkey, next month, for talks with Poroshenko, the White House announced.

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.

Dozens of rockets fired by pro-Russian insurgents could be heard blasting from the city of Donetsk towards a nearby Ukrainian military base, AFP correspondents said.

More shelling was reported near the government-held coastal city of Mariupol, while military authorities reported the deaths of two soldiers in a rebel attack on Sunday near Lugansk.

Kiev and its Western backers see the six-month uprising, and the March annexation by Russian troops of Crimea, as an attempt by Russian President Vladimir Putin to cripple Ukraine.

But 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, fuelling the kind of East-West tensions last seen in the Cold War.

EU member state representatives will on Tuesday review their sanctions, but officials said there was little likelihood of any change for the time being.

Sunday's election was meant to finalise a revolution that began in February, when huge street protests ousted Moscow-backed president Viktor Yanukovych after he abruptly rejected a landmark EU pact.

Communists and other Yanukovych allies were routed Sunday, although a party made up of his former associates won a small share of seats through proportional representation.

Radicals who rejected Poroshenko's peace deal with the insurgents did poorly, as did corruption-tainted politicians who had steered Ukraine through two decades of stuttering reforms.

"Poroshenko and his government will have a difficult time resolving the task of moving into Europe," Yuriy Romanenko at the Stratagema think-tank told AFP.

"The war will also go on for a long time. The standoff there could continue for several years."

Poroshenko says there can be no military victory against the separatists and that he is ready to negotiate autonomy, though not independence, for pro-Russian regions.

A Moscow-backed truce agreement signed by Kiev and the separatists on September 5 calmed the worst fighting, despite frequent violations, especially around the disputed Donetsk airport.