By Richard Balmforth and Pavel Polityuk
KIEV, Dec 9 (Reuters) - Ukraine's military accused separatists of violating an agreed "Day of Silence" in the country's embattled east on Tuesday, an initiative that was seen as an attempt to forge a durable ceasefire paving the way to a new round of peace talks.
In a step towards normalization, Russia resumed shipments of natural gas to Ukraine on Tuesday after a six-month shut-off caused by a dispute over price and debt that ran parallel to the war waged by pro-Moscow rebels in eastern Ukraine.
Government forces said they had suspended combat operations from 10 a.m. on Tuesday and separatists said that the ceasefire was, for the moment, holding.
But as night fell, Kiev's military said troops had recorded 13 violations by rebels shelling Ukrainian positions, highlighting two artillery attacks on the airport of rebel-held Donetsk. It did not say if any soldiers had been killed.
"Not having any idea of observing the agreements, the rebels employed light weapons, mortars and artillery, armored tanks in residential areas," the press service for Kiev's military operation in the east said in a post on Facebook.
The Ukrainians saw the Day of Silence as a litmus test of the Moscow-backed separatists' readiness to reinforce a September truce that has been regularly breached, with almost daily deaths among government forces, rebels and civilians.
Fighting in the past few weeks has been intense around the international airport in Donetsk, the separatists' main urban stronghold. The rebels are trying to wrest the ruins of the airport from government control.
It had been hoped that the truce could improve prospects of a new round of peace talks in the Belarussian capital Minsk involving Russia, Ukraine and the separatists under the auspices of the Organization for Security and Cooperation in Europe.
Talks by that "contact group" in Minsk in early September led to a 12-point blueprint for peace, including a ceasefire.
Since then, however, separatists have defied Kiev by holding elections for officials. Ukraine accuses Russia of sending more troops and weapons to aid the rebels.
"We have declared a Day of Silence three times in the past. This is the fourth time. One hundred and ninety-two people have been killed since Sept. 5," army chief of staff Viktor Muzhenko told journalists in Kiev.
Moscow, which denies its troops are fighting in Ukraine although scores of them have died there, says Kiev has violated the Minsk deal by continuing to fight.
Polish Prime Minister Ewa Kopacz urged the European Union to prepare to impose a third round of economic sanctions on Russia if the Minsk agreement is not fulfilled.
In Donetsk, rebel leader Alexander Zakharchenko said he had ordered his forces to cease firing from 10 a.m. and only to respond if attacked. "The ceasefire for the moment is being observed," he said.
The United Nations says more than 4,300 people have been killed in eight months of conflict that began after a Russian-backed president was ousted by street protests in February.
Russia has annexed Ukraine's Crimea peninsula and given support to separatists in the east, driving relations between Moscow and the West to the lowest point since the Cold War.
Russian Foreign Minister Sergei Lavrov confirmed that a meeting of the contact group was planned in coming days but said an easing of tensions in eastern Ukraine remained "a long way off."
INDEPENDENCE IN ENERGY
The restoration of flows of gas from Russia, after an upfront $378 million payment by Kiev for supplies this month, brings temporary relief to a national power grid short of coal and under further pressure from sudden freezing temperatures.
It also suits Moscow, which wants an uninterrupted flow of gas over Ukraine to supply its European customers in winter.
But a temporary resolution to their gas dispute does little to resolve the separatist war. Ukrainians have accused Moscow of seeking to impose a "frozen conflict" that could keep eastern provinces beyond Kiev's control indefinitely. Moscow and the rebels now call eastern Ukraine "New Russia."
Ukrainian Prime Minister Arseny Yatseniuk said in a speech on Tuesday that the former Soviet republic's sovereignty hinged on achieving "independence in energy."
In comments likely to be seized on by Moscow to justify Russian policy, he also said Ukraine would act to scrap its neutral "non-bloc status," introduced by ousted president Viktor Yanukovich, and do more to bring its army up to NATO standards.
An IMF mission arrived in Kiev to start a fresh round of talks with Yatseniuk's government linked to a $17 billion loan package that may have to be ramped up due to the financial toll the separatist crisis has taken.
State coffers are at their barest in 10 years and Ukraine needs extra cash to service its debt and make gas payments at a time when the economy is contracting and the hryvnia currency hovers close to historic lows. (Additional reporting by Alessandra Prentice in Kiev, Serhiy Kirichenko in Donetsk and Thomas Grove in Moscow; Writing by Richard Balmforth; Editing by Mark Heinrich)