Ukraine and pro-Russian insurgents prepared to put to the test a comprehensive truce on Tuesday aimed at calming an upsurge of violence that has further eroded trust between Moscow and the West.

Local authorities on Monday reported the deaths of at least 12 civilians over a bloody weekend in which government forces and organised militias exchanged volleys of Grad rocket fire across the devastated industrial east.

German Chancellor Angela Merkel -- once one of Europe's more moderate voices on Russian affairs -- blamed the unrest on attempts by an increasingly isolated Kremlin to halt eastern Europeans in their drive toward the EU.

Russia's violation of "the territorial integrity and sovereignty of Ukraine must not be allowed to stand," Merkel told Germany's Die Welt newspaper.

She also defended the sanctions that Brussels and Washington have slapped on Russia for its alleged attempts to splinter its western neighbour in reprisal for the February ouster of a Moscow-backed president.

Russia has struck back by banning Western food imports and imposing other restrictions that have hurt European farmers and provoked a minor rebellion from businesses in countries such as France and Germany.

The diplomatic war of words and jostling for position has intensified as the prospect of new Ukrainian peace talks nears.

"The desire to rip (ex-Soviet republics) away from Russia has always been one of America's top foreign policy priorities," Russian Deputy Foreign Sergei Ryabkov told a session of parliament.

"But since the start of the year, this desire has surfaced with renewed strength and in an especially aggressive manner," the RIA Novosti news agency quoted Ryabkov as saying.

- 'Day of silence' -

Ukrainian President Petro Poroshenko is hoping that a calm in the east can help him focus on pushing through long-delayed economic legislation that could dig the country out of effective bankruptcy and open the way for more global aid.

He has proclaimed Tuesday to be a "day of silence" across the war zone that will be followed by a withdrawal of heavy weapons from the front line -- should the separatists also put down their guns.

Guerrilla commanders have promised to respect the ceasefire.

But confusion has emerged over the fate of vital peace talks in the Belarussian capital Minsk that Poroshenko hopes to convene on the same day in the presence of Russian and European envoys.

Some rebels said no meeting was possible until Friday -- an apparent attempt to show they will only take part on their own terms.

"We will take part in the negotiations," Donetsk separatist co-leader Denis Pushilin told AFP by telephone.

"But for them to be more successful, they must take place on Friday."

Ukrainian Defence Minister Stepan Poltorak responded by stressing that Kiev's forces intended to halt fire on Tuesday even if the Minsk gathering was delayed for a few days.

"The Ukrainian armed forces are ready for silence," he said during a joint press appearance with visiting Canadian Defence Minister Rob Nicholson.

The Minsk negotiations are supposed to reinforce an earlier peace deal reached in the same city on September 5 that failed to halt the fighting. The United Nations says another 1,000 lives have been lost since.

UN estimates put the total death toll from the eight-month conflict at more than 4,300. But the number of rebels killed has never been firmly established and some believe the true numbers are much higher.

Few analysts believe that Tuesday's truce and any talks that follow will be able to quickly restore calm.

But they also warn that the European Union must make the most of the opportunity to contain an increasingly assertive Russian President Vladimir Putin in case he tries to expand his reach even further into Ukraine.

"The failure to find a political solution to the dispute increases the likelihood that separatist and Russian forces would attempt in the coming weeks to take additional territory (in the east) that has economic value," the Eurasia Group political risk consultancy said.

"The future of eastern Ukraine will ultimately be defined by processes that take place outside the region's border," the London-based European Council on Foreign Relations think tank added.