Moldova went to the polls on Sunday in a crucial parliamentary election that will help determine whether the impoverished ex-Soviet country pursues integration with Europe or returns to Russia's fold.

Polling stations opened at 7:00 am (05:00 GMT), with voters facing a choice between political parties aiming for membership in the European Union and those that back joining Russia in a customs union.

U.S. troops will remain in Poland and the Baltic states through 2015 "to deter Russian aggression," the top U.S. commander for Europe said on Sunday.

"There are going to be U.S. army forces here in Lithuania as well as Estonia and Latvia and Poland for as long as it's required to deter Russian aggression," said Lt. General Ben Hodges, commander of U.S. Army Europe.

Russia expelled several Polish diplomats for spying on Monday, deepening the worst East-West crisis since the Cold War as the EU eyed fresh sanctions against Moscow over the violence in Ukraine.

Fresh bloodshed in Ukraine between pro-Kremlin rebels and Kiev's forces added to the tensions after Russian President Vladimir Putin left a G20 summit in Brisbane early amid criticism from western leaders.

Polish hooligans clashed with police Tuesday on the sidelines of the nationalist right's annual march through central Warsaw to mark Poland's independence day. 

A Polish court decided Tuesday that former Serbian police chief Sreten Lukic, who was convicted of committing war crimes in Kosovo, can serve out his 20-year sentence in a Polish prison.

The court in the capital Warsaw however requested more information on the health of another Serbian war criminal, Vladimir Lazarevic, who was sentenced to 14 years behind bars.

NATO member Poland said Tuesday it will acquire combat drones as part of a multi-billion-euro revamp of its armed forces amid heightened tensions with Russia over its role in the Ukraine crisis.

"We will use these drones to defend our territory," Deputy Defense Minister Czeslaw Mroczek told AFP.

NATO member Poland on Monday invited manufacturers of short-range surface-to-air missiles for technical talks for a planned military revamp amid heightened tensions with Russia.

The defense ministry said the new acquisitions will be part of a planned anti-missile shield and air defense system which is pegged to cost 7.1 billion euros ($8.8 billion).

The death toll from a methane explosion at a Polish coal mine rose to five after two gravely burned miners succumbed to their injuries overnight, the hospital treating them said on Tuesday.

One worker had died in the accident on October 6 at the Myslowice-Wesola mine in southern Poland and 28 were hospitalized with severe burns.

Poland on Monday urged NATO's new secretary general to push ahead with a missile shield system amid the West's worst standoff with Russia since the Cold War.

"We firmly support the creation of this (missile shield) system as a pan-NATO one because only this makes deep sense both politically and in terms of defense," Poland's President Bronislaw Komorowski said at a joint press conference with NATO Secretary General Jens Stoltenberg.

Poland on Monday said a possible French deal to supply Russia with warships was making it difficult for Warsaw to choose French suppliers for its planned missile shield.

"I can't hide the fact that the Mistral (warship contract) is not helping us make positive decisions" about French missile shield suppliers, Polish Defense Minister Tomasz Siemoniak said in an interview published in the Rzeczpospolita daily.