CIVILIANS on both sides have been killed in heavy fighting in eastern Ukraine as an attempt to reopen peace talks in neighbouring Belarus was aborted before it began.

Two rebel delegates flew to the Belarus capital Minsk, only to announce that talks would not take place and they were flying back to Moscow. Any talks would be the first since a five-month-old ceasefire collapsed with a new rebel advance last week.

The main rebel stronghold Donetsk echoed to the sound of heavy artillery fire, including salvoes from multiple rocket launchers and heavier thuds from artillery coming from the direction of the airport, a constant battlefield.

Seven people were killed in artillery strikes on a cultural centre and a trolleybus.

Kiev claimed the shelling was carried out by the rebels themselves to ruin the chance of peace talks. Both sides have made similar allegations throughout the conflict, which are impossible to verify.

The head of Ukraine's regional police said seven other civilians had been killed and ten injured as a result of fighting in an around the government-held small towns of Debaltseve and Vuhlehirsk, focus of the rebel advance.

Water and electricity have been cut off in the towns, where government garrisons are all but encircled by rebel fighters.

Kiev's military said five of its servicemen had been killed and 23 wounded in fighting, describing the situation in the conflict zone as "hard".

"They are repeatedly using Grad (missiles), artillery, mortars, tanks and rocket launchers," spokesman Andriy Lysenko said in a televised briefing.

The past week has seen by far the worst fighting in Ukraine since the ceasefire was signed five months ago, with the rebels announcing an offensive that Kiev says amounts to a full repudiation of the truce.

Nato and Kiev accuse Russia of sending thousands of troops to support the rebel advance with heavy weapons and tanks. Moscow denies it is directly involved in fighting over territory the Kremlin refers to as "New Russia".

European Union foreign ministers agreed at an emergency meeting on Thursday to extend for another six months economic sanctions against Russia that had been due to expire soon. Washington has promised to tighten its own sanctions, which have helped feed an economic crisis in Russia.

The arrival of rebel negotiators in Minsk, where last year's ceasefire was first reached as part of a peace deal in September, was the first sign of a reopening of negotiations since the rebels launched their latest advance.

But neither Kiev nor Moscow confirmed that they were ready for talks, and one of the rebel officials, Denis Pushilin, swiftly announced they were heading back to Moscow. He said the rebels were prepared to press on with their offensive and seize more territory if artillery continues to fall on Donetsk and other cities they control.

The immediate fear of Kiev and its Nato allies is of a rebel offensive on Mariupol, a port of 500,000 people which is by far the biggest government-held city in the two restive provinces.

It was hit by shelling on Saturday which Kiev said killed 30 civilians, although the rebels have since denied that it is a target for now. The rebels halted at its gates during their last big advance five months ago.

The rebels have said their principal aims in the advance are to push government guns out of range of their cities, and make their positions more secure by "straightening out the front" - choking off a government-held pocket around Debaltseve.

Both are moves that would make existing rebel areas more defensible over the long term, if, as many Western countries say they suspect, Moscow's aim is to pursue a stable "frozen conflict" in eastern Ukraine.

A rebel assault on Mariupol, with the potential to unleash unprecedented urban warfare, is a far more dangerous prospect. While the rebels say they are not trying to capture it yet, they have repeatedly said they reserve the right to do so, a threat they may be holding out to obtain better terms at talks.