Russia endorsed a crushing victory for Ukraine's pro-Moscow rebel leadership after controversial polls on Sunday that the EU slammed as a "new obstacle" for peace in the country's strife-torn east.

The swift acceptance of the results by Russia looked certain to spark a diplomatic firestorm, with a fresh round of Western sanctions against the Kremlin now increasingly on the cards.

The Ukrainian military on Sunday reported "intensive" movement of troops and equipment from Russia into the separatist controlled parts of eastern Ukraine.

"There is intensive deployment of military equipment and personnel of the enemy from the territory of the Russian Federation onto territory temporarily controlled by insurgents," Ukrainian military spokesman Andriy Lysenko told a briefing in Kiev.

Shelling in eastern Ukraine's rebel-held eastern regions killed five people over the past 24 hours, local authorities said Saturday, in the latest deadly violations of a ceasefire.

"As a result of military actions in Donetsk on October 10, three civilians died and four more were injured and hospitalized," said the mayor's office in Donetsk, the largest eastern city.

Five civilians were killed during intensified shelling in the eastern Ukrainian city of Donetsk, local authorities said Thursday. 

Ukrainian troops and pro-Russian forces were engaged in fresh clashes in the eastern city of Donetsk on Friday as they traded blame over the death of a foreign aid worker four weeks into their shaky truce.

Pro-Russian separatists in eastern Ukraine and authorities in Kiev are planning to hold talks on energy in the region as winter looms over the strife-torn territory, a separatist leader told Agence France-Presse Thursday.

"These discussions will be about vital infrastructure, including about coal and electricity," Andrei Purgin, deputy prime minister of the self-proclaimed Donetsk People's Republic, told AFP by phone. "They need our coal."

Fierce gunbattles erupted around the Ukrainian rebel stronghold of Donetsk on Wednesday, with two civilians killed just a day after lawmakers in Kiev held out an offer of self-rule to the pro-Russian separatists.

Ukrainian riot police fired tear gas on a group of about 200 demonstrators protesting outside parliament to demand the adoption of a so-called lustration law.

At least one activist from the Right Sector nationalist group was injured in the brief clashes, which saw protesters -- some masked -- set tires ablaze in Kiev, an AFP photographer said.

U.S. President Barack Obama said Thursday that the United States would intensify sanctions in the defense, finance and energy sectors to punish Russia over its "illegal actions" in Ukraine, as the European Union said it could lift a new set of sanctions if a Ukraine ceasefire holds.

Obama said in a statement the move would worsen the Kremlin's deepening political and economic isolation.

A Ukrainian fighter jet has been shot down by a Russian anti-aircraft system in the east of the country, where Kiev is fighting pro-Moscow rebels, Ukraine's military said on Saturday.