Ukraine on Sunday mourned 49 people killed when pro-Kremlin rebels downed their military plane as Kiev prepared to host last-gasp talks with Moscow to avert a Russian gas cut that would also hit Europe.
Flags were lowered across the crisis-hit nation while television stations inserted an image of a burning candle into their frames after Ukrainian forces suffered the single biggest loss of life in their escalating two-month push to reclaim control of separatist areas of the industrial east.
But the gas negotiations and commemorations were both clouded by a new diplomatic feud that exploded after an irate Ukrainian mob in Kiev smashed the Russian embassy's windows and overturned cars while the police looked on.
Ukraine's new more nationalistic leaders and their Western allies accuse Russia of supplying weapons and even tanks to the insurgents in a bid to break up its western neighbour following the February ouster of a pro-Kremlin regime.
NATO released satellite images purporting to show three Russian tanks that had crossed the border and were later spotted being raced across the eastern city of Donetsk by militants flying the flag of their self-declared "People's Republic".
But Moscow has hit back by accusing Western powers of backing dangerous Ukrainian "fascists" who are prosecuting the east's ethnic Russians and waging a "punitive operation" against their own people.
The third "gas war" between Russia and Ukraine since 2006 flared when Moscow nearly doubled its rates in the wake of the deadly winter uprising that now threatens to pull Kiev out of the Kremlin's historic orbit for the first time.
Ukraine receives half its gas supplies from Russia and transports 15 percent of the fuel consumed in Europe -- a reality that prompted EU Energy Commissioner Guenther Oettinger to try to urgently broker a long-term solution to the dispute.
- Final offer -
Kiev said heading into the negotiations that it was ready to make a $1.95 billion (1.45 billion euro) payment demanded by Moscow if Russia agreed to cut its ongoing price to $326 from $485.50 for 1,000 cubic metres of gas.
But Russian President Vladimir Putin says $385 per 1,000 cubic metres is his final offer and has threatened to turn off Ukraine's taps if no payment was made by 0600 GMT Monday.
The negotiations broke up after just two hours late Saturday without a hint of a comprise.
"No solution was found," Ukrainian Energy Minister Yuriy Prodan told reporters outside the plush central Kiev hotel hosting the high-stakes meeting.
A spokeswoman for Ukraine's Naftogaz state energy company said Sunday's round should begin at 1600 GMT after sides failed to meet in the morning as originally planned.
- 'Hands off Ukraine' -
Ukraine's newly-elected President Petro Poroshenko tapped into the fury provoked by Saturday's plane downing near the eastern city of Lugansk by vowing to deal the insurgents "an adequate response".
His comments were soon followed by what appeared to be a spontaneous protest outside the gated Russian embassy compound in Kiev that soon turned violent.
Nationalists with signs reading "Kremlin -- hands off Ukraine!" climbed the perimeter fence while others smashed the building's windows with boulders and overturned diplomats' cars.
One man managed to pull down the Russian national tricolour with a long metal pole while about a dozen police officers looked on before simply leaving the scene.
The Russian foreign ministry called the lack of a police response "a grave violation of Ukraine's international obligations" and accused Europe of condoning the attack.
"Oh, how the (Ukrainians) are trying to pull us into a war," lower house of parliament's foreign affairs committee chairman Alexei Pushkov tweeted.
Washington also delivered Kiev a rare rebuke by urging "authorities to meet their Vienna Convention obligations to provide adequate security".
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'Extreme concern'German Chancellor Angel Merkel and French President Francois Hollande expressed "extreme concern" over the spiralling violence in a joint phone conversation with Putin in which they stressed the importance of rapidly reachuing a ceasefire.
But the rebels responsible for shooting the Il-76 transporter out of the sky vowed to fight the Ukrainian forces until they were driven out of the coal and steel producing region for good.
"They brought machine guns and ammunition," a rebel commander name Mudzhakhed said while examining the charred remains of the plane in a wheat field outside Lugansk.
"They knew where they were flying and they were warned," said another man who identified himself only as Roman.
"We are the people of Lugansk. Ukraine does not exist anymore."