Western countries are trying to use the Ukraine conflict to topple President Vladimir Putin and wreck Russia's economy, the president's spokesman said in an interview published on Wednesday.

"In the West they are trying to kick out Putin, to isolate him in international politics, to throttle Russia economically due to their interests, to bring down Putin," Kremlin spokesman Dmitry Peskov said.

Heavy fighting raged between Ukrainian forces and pro-Russian rebels in the country's war-torn east Wednesday, killing at least five more civilians ahead of high-stakes peace talks in Berlin.

Explosions shook the battered city of Donetsk after days of fighting left an already shaky September truce in tatters.

Ukraine on Tuesday accused Russian forces of attacking its soldiers after crossing over into the ex-Soviet state's war-wrecked separatist east in violation of a September truce deal.

The charges -- met with initial silence by Moscow -- should add further tensions to difficult talks in Berlin on Wednesday aimed at stemming a spike in fighting that has already killed 4,800 people and driven a million from their homes.

Ukraine on Tuesday accused Russian forces of attacking its soldiers after crossing over into the ex-Soviet state's war-wrecked separatist east in violation of a September truce deal.

The charges -- met with initial silence by Moscow -- should add further tensions to difficult talks in Berlin on Wednesday aimed at stemming a spike in fighting that has already killed 4,800 people and driven a million from their homes.

The foreign ministers of Ukraine, Russia, Germany and France are set to meet Wednesday in Berlin in a bid to de-escalate the Ukraine conflict, Germany said.

"The chief aim now is to prevent a further deterioration of the military conflict and a renewed political escalation between Kiev and Moscow. This is worth every effort," German Foreign Minister Frank-Walter Steinmeier said in a statement.

Russian-backed insurgents on Tuesday assaulted the remnants of a Ukrainian force hanging onto a ruined airport near the rebels' main stronghold as Moscow poured cold water on the prospect of peace talks.

Blasts of incoming and outgoing artillery echoed all night across Donetsk -- a once bustling industrial city but now the crucible of one of Europe's worst humanitarian and diplomatic crises since the Cold War.

Russia on Tuesday denied as "absolute nonsense" the latest accusations by Kiev that Moscow had sent hundreds of troops over the border into Ukraine.

"Yesterday's accusations from Kiev of the alleged deployment of Russian army contingents across the Russian-Ukrainian border do not stand up to any criticism," defense ministry spokesman Igor Konashenkov said, Russian news agencies reported.

EU foreign ministers agreed Monday there would be no change in the bloc's Russia policy, including sanctions, as the union's diplomatic chief warned the Ukraine situation had got "much worse" in recent weeks.

They said they would stick to their course until Russia fully implemented the Ukraine peace accords it had backed in September, despite EU foreign policy chief Federica Mogherini's suggestion of a review in the way the European Union deals with Russia.

Sporadic shelling hit a hospital in Donetsk and shook other parts of the region on Monday while Ukraine alleged that hundreds of Russian troops crossed the border to help rebels fighting for control of the country's east.

Ukraine's fresh charges of Russia backing the rebels comes after each side blamed the other for a complete breakdown of a September truce in recent days, with heavy combat having rocked the area around Donetsk airport.

Fighting eased in the Donetsk region on Monday after Ukraine launched a major offensive and claimed to clear pro-Russian rebels from most of the airport outside the key eastern city.

There were a number of sporadic explosions overnight, but the violence seemed to be far less than in previous days, when heavy clashes shook the area around the airport and shelling moved closer toward the city center, killing at least 10 civilians.