Violence has intensified in eastern Ukraine, casting doubt over the prospects for a planned international summit on the conflict, while Kiev seeks urgent financial help for its ailing economy.

The Ukraine military say shelling on Friday killed four servicemen and two civilians near Donetsk airport. The airport has been at the centre of fighting which has so far resulted in more than 4,700 deaths and created around one million refugees.

The airport has been at the centre of fighting which has resulted in more than 4,700 deaths and created around 1 million refugees.

Ukraine's government in Kiev and the separatist rebels blamed each other for the artillery fire.

Violence has escalated in recent days, after a month of relative calm which followed a truce deal that built on the 5 September ceasefire was agreed in Minsk, Belarus.

That pact is still seen by Ukraine and its western allies as a basis for resolving the conflict. On 29 December Ukraine's president Petro Poroshenko announced plans to hold talks on the crisis with the leaders of Russia, Germany and France in Astana, Kazakhstan, on 15 January. The summit is yet to be confirmed.

Yesterday Kazakh leader Nursultan Nazarbayev discussed the meeting with German Chancellor Angela Merkel during a visit to Berlin. He also spoke by telephone to Russian President Vladimir Putin. In a conference

In a conference call on Friday, the foreign ministers of Ukraine, Russia, Germany and France agreed to meet in Berlin on Monday to discuss the Kazakhstan summit.

On Thursday, German Foreign Minister Frank-Walter Steinmeier said the four leaders should only meet in Kazakhstan, if they considered that tangible progress could be made. However, on Friday Germany's foreign ministry stated that all the states involved should do their utmost to restart the stalled peace process.

Ukraine officials have tied the upsurge in the fighting to fresh supplies of weapons, allegedly provided by Russia, which were received earlier this week.

The Russians insist their latest relief convoy only carried civilian supplies. Kiev and western powers reject Moscow's claim that it is not providing military help to the rebels. They are demanding that Russia fulfil a promise to close its border with eastern Ukraine, in order to stop the flow of fighters and weapons to the separatists.

On Thursday Merkel said she had "little hope" that western sanctions imposed on Russia after its annexation of Crimea would be lifted. She added that other sanctions could be cancelled only if "the entire Minsk agreement is fulfilled".

The upsurge in violence comes as officials from the International Monetary Fund are in Kiev discussing the disbursement the next tranches of a $17bn (£11.24bn) aid package for Ukraine.

Meanwhile, Hungarian-born billionaire hedge fund manager George Soros is calling on the EU to provide a $50bn package to Ukraine as a safeguard against Russian aggression.