A fierce battle erupted Monday for control of the main airport in rebel-held eastern Ukraine, just hours after future president Petro Poroshenko vowed he would not let the country become another Somalia.
Ukrainian fighter jets and combat helicopters struck at separatist gunmen who seized the airport in the main city of Donetsk, triggering heavy gunbattles.
It was the most forceful action by the Kiev government in its battle to crush a bloody pro-Moscow insurgency that has raged in the industrial east since early April, threatening to tear apart the former Soviet state.
Plumes of thick black smoke rose from the airport complex as the sound of explosions and heavy machinegun fire rang out, AFP correspondents at the scene said.
Scores of gunmen had stormed the airport early Monday in an apparent show of defiance against Poroshenko, the Ukrainian oligarch who claimed a resounding victory in Sunday's presidential election.
Poroshenko has moved swiftly to stamp his authority as Ukraine's new leader, and the country's former masters in the Kremlin said Monday they were ready to work with him.
The 48-year-old billionaire and former cabinet minister said Ukraine would press on with its offensive against the insurgents who now control about a dozen cities and towns, despite Moscow warning it would be a "colossal mistake".
"There are no talks with terrorists," said the centrist pro-Western tycoon known as the chocolate king for his confectionary empire.
"Their goal is to turn Donbass (east Ukraine) into Somalia. I will not let anyone do this to our state and I hope that Russia will support my approach."
Sunday's vote was seen as the most important in Ukraine's post-Soviet history as it fights to stay united after months of turmoil and avert economic collapse.
But the insurgency, which has already cost at least 150 lives, thwarted polling in much of the east and rebels have defiantly refused to recognise the vote.
- 'Pragmatic dialogue' -
Russia, which has been threatened with a new round of Western sanctions if it meddled further in Ukraine after its seizure of Crimea in March, said it was willing to work with the new leaders.
"We are ready for pragmatic dialogue, on an equal footing, based on respect for all agreements, in particular in the commercial, economic and gas spheres," Foreign Minister Sergei Lavrov said in the Kremlin's first reaction.
"As the president (Vladimir Putin) has said, we respect the result of the choice of the Ukrainian people."
But he said Kiev's plans to pursue operations against the insurgents who have declared independent states in two regions in the east would be a "colossal mistake", and called on the new government to open talks.
The latest results give Poroshenko close to 54 percent of the vote, far ahead of his nearest rival, the divisive former prime minister and Orange Revolution leader Yulia Tymoshenko with 13 percent.
It also means he should avoid the need for a June 15 runoff that would have extended political uncertainty and put more pressure on East-West relations that are already at a post-Cold War low.
Final results are expected later Monday.
Observers with the Organisation for Cooperation and Security in Europe said the election "largely upheld democratic commitments" and provided the new leader with legitimacy despite the problems in the east.
While turnout was strong across the capital Kiev and the more pro-European west on Sunday, voting was largely blocked in two eastern regions that make up 15 percent of the electorate.
"We consider that the winner of the election is president of west Ukraine -- he is a half president," said pro-Russian presidential candidate Oleh Tsarov.
- 'Courageous Ukrainians' -
The election commission said voting had been suspended by militants in 24 of Ukraine's 213 constituencies.
But US President Barack Obama praised "courageous Ukrainians" for voting in the face of the threat posed by the militants.
The ballot was called after Kremlin-allied president Viktor Yanukovych -- his corruption-stained regime long a source of discontent -- was ousted in February in the bloody climax of months of protests sparked by his rejection of a historic EU pact.
Putin responded by seizing Crimea and threatening to invade the rest of Ukraine to "protect" the country's ethnic Russian community, raising the prospect of all out war on Europe's doorstep.
But Russia said last week it had started withdrawing from Ukraine's border around 40,000 soldiers whose presence had raised deep Western suspicions and prompted NATO to send additional fighters to former Soviet satellite states.
In addition to the political and security challenges ahead, Poroshenko will have to adopt painful austerity measures that world lenders are demanding in return for $27 billion (20 billion euros) in aid to prevent bankruptcy.
He will also have to negotiate with Russia over key gas supplies after the Kremlin said it would cut shipments by early June if Kiev does not pay a bill.