The Red Cross on Saturday denied involvement in a Russian "humanitarian convoy" that Ukraine claimed to have stopped from crossing the border over fears it was an attempt by Moscow to invade the ex-Soviet state.

The charity said while it had received an offer from Moscow to organize aid convoys, and would welcome any effort to ease civilian suffering in the region, no such action had taken place.

Fierce battles on Ukraine's porous eastern border left 15 government troops dead as fears of a possible Russian invasion swirled on Friday despite NATO urging Moscow to withdraw its troops along the frontier.

International tensions also rose as Western countries slammed a Russian food embargo imposed as revenge for sanctions slapped on Moscow over its backing for insurgents in Ukraine.

WikiLeaks founder Julian Assange urged U.S. intelligence leaker Edward Snowden on Thursday to watch his "physical security" if he travels abroad after Russia gave him a residence permit.

Snowden, a former U.S. intelligence operative who is wanted by the United States on espionage charges, was granted three-year residency by Moscow, allowing him to travel abroad, his lawyer said.

NATO chief Anders Fogh Rasmussen urged Russia to "step back from the brink" during a visit to Kiev on Thursday and vowed support for Ukraine as fears mounted that Moscow was preparing to send troops into the conflict-torn east of the country.

His visit came as the center of the main rebel bastion Donetsk was hit by sustained bombardment for the first time in four months of fighting, and a dozen civilians were killed around the region.

Thick smoke from burning tires once again billowed into the blue sky over Kiev's iconic Independence Square on Thursday as a rump of demonstrators still living in the protest camp scuffled with authorities trying to clear the area.

Dozens of demonstrators hurled stones and set debris alight as they halted a short-lived push by municipal workers backed by interior ministry troops to dismantle barricades around the entrance to the central square with bulldozers.

Fugitive U.S. intelligence operative Edward Snowden has been granted a three-year residence permit in Russia, his lawyer said on Thursday, in the latest blow to Moscow's deeply strained relations with Washington.

"The request was accepted and accordingly Edward Snowden was given a three-year residence permit" which allows him to move about freely and travel abroad, lawyer Anatoly Kucherena told journalists.

Russia retaliated against tough new Western sanctions on Thursday, banning most food imports from the United States and the European Union and threatening to block flights over its airspace.

The 28-member European Union swiftly denounced the measures -- which also target Canada and Australia -- and said it was ready to take action in response.

President Barack Obama says that U.S. sanctions levied against Russia over its actions in Ukraine are working but that Washington would face a much different set of questions about how to respond if Moscow invaded eastern Ukraine.

Western officials warn that a Russian military buildup on Ukraine's border could herald a major incursion to protect the pro-Moscow separatists fighting Ukrainian forces. Despite bipartisan pressure from lawmakers to send U.S. military aid to Ukraine, however, the Obama administration thus far has said it doesn't believe U.S. military assistance is needed.

A Russian deputy economy minister was sacked Wednesday after criticizing "stupid" government economic policies in an online post that went viral.

Sergei Belyakov, a deputy economy minister since 2012, apologized in the note for the government's decision to use money from pension funds to plug holes in the budget.

International experts have suspended their search for body parts at the MH17 crash site on Wednesday because of deteriorating security in eastern Ukraine, Dutch Prime Minister Mark Rutte said.

"It doesn't make sense to continue with the repatriation in this manner," the Dutch leader told a press conference in The Hague.