By Richard Balmforth
KIEV (Reuters) - Ukraine plans a "Day of Silence" on Tuesday to try to rebuild a ceasefire with pro-Russian separatists that has all but disintegrated, but accompanying peace talks -- the first in three months -- look likely to be delayed.
On the eve of the planned resumption of negotiations to end months of fighting between the rebels and Ukrainian troops in eastern Ukraine, authorities in the Belarussian capital Minsk, where they were due to be held, said they had not been told whether the Ukrainians would attend.
In Moscow, President Vladimir Putin's top foreign policy adviser said the talks, which Ukrainian President Petro Poroshenko had said were penciled in for Tuesday, should take place in Minsk "this week".
They would be the first since a 12-point ceasefire plan was worked out there in early September under the auspices of the Organization for Security and Cooperation in Europe (OSCE), to try to end the worst crisis between the West and Russia since the Cold War.
That ceasefire has been continually flouted, with hundreds of civilians, separatists and Ukrainian troops killed and allegations from Kiev that Moscow had failed to pull out Russian fighters and military equipment supporting the separatists.
While Putin's adviser Yuri Ushakov said Russia would do everything it could to enable the talks to go ahead this week, Ukrainian Prime Minister Arseny Yatseniuk urged Moscow to fulfil its obligations under the September deal.
"If Russia continues its aggressive policy towards Ukraine and the whole world, it will have to continue paying the price," Yatseniuk was quoted as saying by his news service, referring to Western sanctions against Russia.
Despite this, Russia was expected on Thursday to resume some deliveries of natural gas to the former Soviet republic halted six months ago in a row over prices and debts, complicated by the war in the east, after Kiev approved an upfront payment.
Ukrainian Defence Minister Stepan Poltorak said the two sides had reached a "preliminary agreement" to cease fire in a "Day of Silence" on Tuesday. "We shall see if it is going to be honored," he was quoted as saying by Interfax news agency.
But Moscow, Kiev and the West continued to trade accusations over Russia's annexation of Crimea and its support for the separatists in a conflict that has killed more than 4,300 people.
In Moscow, a senior Russian diplomat accused the United States of trying to bring down Putin by sanctions and bring about "regime change".
"It is hardly a secret that the goal of the sanctions is to create social and economic conditions to carry out a change of power in Russia," deputy foreign minister Sergei Ryabkov told a hearing in the lower house. "There will be no easy or fast way out of this."
In Kiev, visiting Canadian Defence Minister Rob Nicholson, whose NATO country has donated non-lethal military aid and winter clothing to Ukraine's pro-Western government and military, said: "We have to continue to maintain the pressure on Russia so they start to comply with international law. They should discontinue their actions and make amends to Ukraine."
German Chancellor Angela Merkel said it might take a lot longer than previously envisaged to reach a diplomatic solution. "We're going to need more patience than we first imagined," she told ARD television.
Ukrainian military spokesman Andriy Lysenko, announcing that another Ukrainian soldier had been killed in the past 24 hours in clashes, said: "We hope that these talks (in Minsk) will give the enemy the chance (to stop firing) and give the OSCE the opportunity of drawing conclusions and determining who is violating the ceasefire."
Much has changed in the east since the last round of talks in Minsk of the "contact group" which normally brings together a former Ukrainian President, Moscow's ambassador to Kiev, an OSCE representative and separatist leaders.
Since September, the separatists have declared "people's republics" and elected officials. On the battlefield, separatist assaults have continued on the main international airport in the main city of Donetsk to wrest control from government forces.
The rebellion has destroyed infrastructure in Ukraine's east, wrecked the economy and eaten away at its foreign currency reserves which are at a 10-year low.
Now that Kiev has finally formed a government, a mission from the International Monetary Fund, one of Ukraine's biggest lenders, is due to visit Kiev from Tuesday to discuss economic reforms that could unlock further credits under a $17 billion bail-out.
(Additional reporting by Katya Golubkova and Maria Kiselyova in Moscow, and Pavel Polityuk and Alessandra Prentice in Kiev; editing by Philippa Fletcher)