Pro-Russian rebels have shot down a Ukrainian military transport plane in the separatist east, killing all 49 troops on board.
Saturday’s attack came hours before top Moscow and Kiev officials were to meet in the Ukrainian capital for 11th-hour gas negotiations aimed at averting a cut in Russian supplies that would also impact large swathes of Europe.
The early morning downing near the airport of rebel stronghold Lugansk came a day after Ukrainian forces notched their biggest success in the campaign to reunify the splintered nation by reclaiming control of the strategic southeastern industrial port of Mariupol.
The United States on Friday accused Russia of helping in the insurgency by sending tanks and rocket launchers to the pro-Moscow rebels, a charge denied by the Kremlin.
Closed-circuit footage of the strike showed a small flash flare when the large Il-76 plane was hit by what Ukrainian officials said was heavy-calibre machine gun fire.
About 30 seconds later, a massive second burst of light lit up the horizon when it apparently exploded upon hitting the ground while approaching Lugansk airport.
Vladyslav Seleznyov, a spokesman for Ukraine’s self-proclaimed “anti-terrorist operation”, said the plane was carrying nine crew members and 40 paratroopers.
“They all died,” he said. The four-engine jet was also carrying military equipment.
The Lugansk militants claimed rebel responsibility for the attack, telling Russia’s RIA Novosti state news agency the plane was hit with a surface-to-air missile.
Ukraine’s new Western-backed President Petro Poroshenko immediately vowed to punish the guilty and deliver “an adequate response”.
Ukrainian forces suffered further losses on Saturday when pro-Russian gunmen ambushed a border guard convoy in Mariupol, killing three servicemen and wounding four.
Council of Europe Secretary General Thorbjoern Jagland said he was “deeply concerned” by the attack and Poroshenko could “count on our support”.
Lugansk, an industrial city of 400,000, has been under effective rebel control since the eastern uprising began in early April but Ukrainian forces had managed to hold on to its airport and use it to rotate equipment and troops serving in the campaign.
Yet they have been forced to repel more frequent raids by the gunmen, who had also briefly seized the international airport in the neighbouring rebel-held city of Donetsk in May.
The two-month insurgency is now known to have claimed at least 320 lives of civilians and fighters on both sides.
Poroshenko’s troubles have been compounded by the threat of being cut off from vital Russian gas shipments as early as Monday morning because of a bitter price dispute.
Ukraine receives half its gas supplies from Russia and transports 15 percent of the fuel consumed in Europe. Moscow had nearly doubled the price it charges Kiev for the fuel in the wake of the February ouster of a Kremlin-backed president.