Heavy fighting in eastern Ukraine has killed civilians on both side, while an attempt to reopen peace talks in neighbouring Belarus was aborted before it began.

As the main rebel stronghold Donetsk reverberated with heavy artillery fire on Friday, two rebel delegates flew to the Belarus capital Minsk to announce that planned talks were off before flying back to Moscow.

The talks would have been the first since a five-month-old ceasefire collapsed with a rebel advance last week.

In Donetsk, salvoes from multiple rocket launchers and heavier thuds from artillery came from the direction of the airport, a constant battlefield.

A Reuters cameraman in the city saw four covered bodies near a cultural centre hit by artillery and a fifth dead person in a badly damaged car nearby. A woman was weeping by one of the bodies. Aid was being distributed at the centre when the shell struck.

Half a mile away, a sixth dead person lay where a trolleybus had been hit. The separatists said the total death toll in those two strikes was seven.

Kiev said Friday’s shelling of Donetsk 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.

“We are already used to this artillery and there’s nothing we can do about it. Our boys are defending us,” said Alla, a shopkeeper in downtown Donetsk.

The head of Ukraine’s regional police said in a Facebook post that seven other civilians had been killed and 10 injured as a result of fighting in and 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 in the past 24 hours, 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 fiercest fighting continues around the town of Vuhlehirsk. After mass artillery attacks, the terrorists repeatedly stormed Ukrainian army checkpoints.”

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 that the Kremlin refers to as “New Russia”.

EU foreign ministers agreed at an emergency meeting on Thursday to extend economic sanctions against Russia for another six months. 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.

“If shelling resumes, then we reserve for ourselves the right to continue the offensive and go to the very borders of Donetsk and Luhansk regions,” he said, referring to the two provinces where separatists have declared people’s republics.