Russia on Thursday broadened a food embargo imposed in retaliation for Western sanctions over Ukraine to include Iceland, a significant fish importer, as well as Montenegro, Albania and Liechtenstein.

Prime Minister Dmitry Medvedev said Ukraine will be added to the embargo from January 1 next year when a landmark EU-Ukraine trade deal enters force, unless Kiev makes a deal with Moscow.

Kiev on Thursday said two soldiers had been killed in the heaviest clashes since the signing of a February truce deal with pro-Russian insurgents in Ukraine's separatist east.

Ukrainian National Security and Defense Council Secretary Oleksandr Turchynov said militants had shelled government positions 153 times across the war zone.

Ukraine on Wednesday reported intense battles with pro-Russian insurgents near the last major government stronghold in the former Soviet country's separatist east.

A military spokesman in Kiev said clashes north of the Sea of Azov port of Mariupol had killed one soldier and injured three.

Investigators probing the shooting down of Malaysia Airlines flight MH17 said Tuesday they had identified possible Russian-made BUK missile fragments from eastern Ukraine, where the plane crashed.

International and Dutch investigators are probing "several parts, possibly originating from a BUK surface-air-missile system," said a joint statement from prosecutors and the Dutch Safety Board (OVV).

Ukraine vowed Tuesday to use all weapons at its disposal to withstand an alleged new pro-Russian rebel advance that added urgency to a goodwill visit by Britain's defense secretary.

Kiev accused the eastern separatist fighters of launching another missile assault north of Mariupol -- a government-held port that provides a land bridge between rebel territories and the Russian-occupied Crimea peninsula.

Ukraine on Monday reported it had repelled a rare tank assault by pro-Russian rebels that threatened to shatter a shaky ceasefire and dangerously escalate the 16-month war in its breakaway east.

President Petro Poroshenko said "about 200 insurgents" had staged a pre-dawn raid on Novolaspa -- a village halfway between the separatists' de facto capital Donetsk and the Kiev-held southern port of Mariupol -- that caught government soldiers off-guard.

OSCE observers based in the separatist stronghold of Donetsk in eastern Ukraine said Sunday that four of their vehicles were destroyed in an apparent arson attack at their hotel.

The Organization for Security and Co-operation in Europe described the attack as aimed at halting its monitoring activities in the separatist region, but stressed that it has no plans to leave.

The United States is further damaging its relations with Moscow by adding a Russian offshore oil and gas field to its sanctions imposed over Ukraine, a Kremlin spokesman said Friday.

"The trend to continue a dialogue in the language of sanctions is further destroying our bilateral relations, unfortunately," President Vladimir Putin's spokesman Dmitry Peskov said, quoted by TASS news agency.

Ukraine on Friday reported the death of two soldiers in continuing clashes following failed talks on bringing an end to the 16-month war in the former Soviet country's pro-Russian east.

Military spokesman Andriy Lysenko said seven servicemen were also wounded but gave no other details.

The value of Russia's beleaguered ruble fell Thursday to more than 70 to the euro for the first time since March, deepening its recent meltdown. 

The ruble also tumbled against the dollar to 64.42, its weakest since the end of February, as the currency continued to drop after a period of relative stability.