Yesterday's violence came as top Russian and Ukrainian officials met for gas talks in Kiev but failed to make immediate progress, agreeing instead to resume negotiations today in a bid to avert an imminent cut in Russian supplies that would also affect large swathes of Europe.
The United States accused Russia of helping the insurgency by sending tanks and rocket launchers to the pro-Moscow rebels -- a charge the Kremlin denied.
The man known to his unit as Mudzhakhed (Sacred Fighter) said the plane tried to dump fuel after the rebels hit its engines. The heavy transporter crashed on its second landing approach after being hit by heavy machine gun fire.
He listed the mostly Russian-speaking region's grievances against the new more nationalist leaders in Kiev.
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"They brought machine guns and ammunition," Mudzhakhed said. "We do not like people telling us what to do."
Poroshenko spoke moments before a crowd of several hundred smashed windows in the Russian embassy building and overturned several luxury cars belonging to its staff before pulling down its tricolour with the help of a wooden pole.
Later they threw a Molotov cocktail, which hit the wall of the building, but was quickly extinguished, according to an AFP reporter on the scene.
Russia condemned Kiev police inaction as "a grave violation of Ukraine's international obligations".