Ukraine is marking a national day of mourning and vowing to retaliate after pro-Kremlin rebels downed a military plane, killing 49, in their deadliest single attack against government forces.
Russia and Ukraine are also meeting for key gas talks on Sunday to avert a cut in Russian supplies that would affect large swathes of Europe.
The talks comes a day after protesters smashed Russian embassy windows in Kiev in the wake of the attack that brought down the transport plane in Ukraine’s east.
The United States accused Russia of helping the insurgency by sending tanks and rocket launchers to pro-Moscow rebels, a charge the Kremlin denied.
A commander in rebel-held Lugansk, where the plane was shot down, showed the transporter’s debris 12km from the airport.
He said the plane tried to dump fuel after rebel fire hit its engines but it crashed on its second landing approach.
Ukraine’s West-backed President Petro Poroshenko vowed to launch “an adequate response” and signalled intensification of the current offensive.
Poroshenko spoke moments before a crowd of several hundred smashed windows in the Russian embassy.
Russia condemned Kiev police inaction as “a grave violation of Ukraine’s international obligations”.
Washington also delivered Kiev a rare rebuke by urging “authorities to meet their Vienna Convention obligations to provide adequate security”.
German Chancellor Angela Merkel and French President Francois Hollande expressed “extreme concern” over Ukraine’s spiralling violence in a joint phone call to Russian President Vladimir Putin.
Lugansk has been under effective rebel control since the eastern uprising began in early April.
On Saturday, three Ukraine border guards were killed and four wounded after an ambush in southeastern Mariupol – captured with great fanfare by federal forces the day before.
Ukrainian forces have so far managed to hold on to Lugansk’s airport and use it in the campaign to quell the separatist unrest.
The eastern insurgency has now claimed at least 320 lives on both sides.
Poroshenko’s troubles have been compounded by the threat of Russian gas shipment cuts as early as Monday in the bitter gas price dispute, which talks on Saturday failed to resolve.
“No solution was found, and the negotiations will continue Sunday morning,” Ukrainian Energy Minister Yuriy Prodan said after EU-brokered talks.
Ukraine receives half its gas supplies from Russia and transports 15 percent of fuel consumed in Europe. Moscow had nearly doubled the price it charges Kiev in the wake of the February ouster of a Kremlin-backed president.
Ukraine said it was ready to make a $US1.95 billion ($A2.11 billion) payment demanded by Moscow if Russia agreed to cut its ongoing price to $US326 ($A353) per 1000 cubic metres but Russia said $US385 ($A417) was its final offer.
The United States on Friday accused Russia of sending tanks and rocket launchers to rebels.
A US State Department spokeswoman raised the prospect of further Western economic sanctions if Russia failed “to demonstrate its commitment to peace”.