Ukraine said on Tuesday that a peace summit President Petro Poroshenko had hoped to convene to end his ex-Soviet republic's separatist uprising would require more preparation and talks with pro-Russian rebels.

The foreign ministers from Moscow and Kiev and their German and French counterparts met in Berlin on Monday to try to save a leadership meeting Poroshenko had proposed holding in the Kazakh capital Astana on Thursday.

Russian President Vladimir Putin has not confirmed his attendance at a crunch peace summit on Ukraine proposed for January 15 in Kazakhstan, the Kremlin said Monday. 

Kremlin spokesman Dmitry Peskov said that Putin's presence at the meeting -- which Ukrainian President Petro Poroshenko hopes will see four-way talks with the leaders of France and Germany -- depends on the outcome of a gathering of foreign ministers in Berlin on Monday.   

Intense fighting erupted around east Ukraine's main rebel-held city on Sunday that wrecked a power station and briefly trapped more than 300 coal miners in one of Europe's largest pits.

Repeated rounds of rocket and mortar fire echoed across snow-covered Donetsk on Sunday evening despite a formal truce in the nine-month war.

Francois Hollande, Angela Merkel and Petro Poroshenko met briefly at the French presidency in Paris Sunday to discuss the Ukrainian crisis before leaving to take part in a historic march against terrorism.

Russia's Foreign Minister Sergei Lavrov, who was also present to attend the demonstration, did not go to the talks, the presidency said.

Poland's foreign ministry said Sunday it was repatriating nearly 200 Polish nationals from separatist regions of Ukraine in the grip of an armed conflict.

"The evacuation of these people from the Donetsk region has entered its decisive phase," said Konrad Pawlik, the deputy foreign minister.

Moscow may ask for early payment on its three billion dollar loan to Ukraine, Russian Finance Minister Anton Siluanov said Saturday, accusing Kiev of violating loan conditions.

"Ukraine has violated the conditions of this loan, specifically that Ukraine's public debt does not surpass 60 percent of its GDP," the minister told Russian news agencies.

Four Ukrainian soldiers and at least as many civilians died Friday in an upsurge of rocket attacks that came just as prospects for international peace talks on the nine-month crisis dimmed.

Local authorities in the rebel stronghold of Donetsk said another nine residents were injured in sporadic clashes that continued from dawn late into the evening around the industrial city's disputed airport.

Four Ukrainian soldiers and two civilians were reported killed Friday in an upsurge in mortar and rocket attacks launched just days ahead of planned international talks on the crisis.

Local authorities in the rebel stronghold of Donetsk said two civilians were killed and seven injured in clashes around the industrial city's disputed airport.

Britain, Denmark, Estonia and Lithuania on Friday urged Brussels to prepare an EU-wide plan to tackle Russia's "propaganda campaign" amid tensions over Ukraine.

"Russia is rapidly increasing its disinformation and propaganda campaign, as an asymmetric response to Western economic power," the countries' foreign ministers said in a letter obtained by Agence France Presse.

The European Union sees some "positive signs" from Russia over the crisis in Ukraine ahead of a mooted summit of key leaders in Kazakhstan, the bloc's foreign policy chief Federica Mogherini said Thursday.

Mogherini insisted however that Moscow would have to meet the terms of last year's Minsk peace agreement before European sanctions imposed over the violence in eastern Ukraine can be lifted.