Ukrainian protesters shout slogans near the Russian Embassy during a rally in Kiev, Ukraine.

KIEV: 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 neighbor 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.

Meanwhile, Russian parliamentarians urged Ukraine on Sunday to sack its foreign minister for using indecent words for Russian president during a violent protest outside Russian Embassy in Kiev.

Acting Foreign Minister Andriy Deshchytsia tried to persuade protesters not to use violence at the rally on Saturday evening, during which the Russian flag was ripped up, vehicles overturned and stones and eggs thrown at the embassy.