Ukrainian forces pounded pro-Russian rebels to the east of the port of Mariupol on Friday, hours before envoys from Ukraine and Russia were expected to announce a ceasefire as the starting point for a wider peace plan.
Ukraine says its forces are trying to repel a big offensive by the rebels to take Mariupol, a port city of around 500,000 on the Sea of Azov crucial for its steel exports. It stands about halfway between Russia and the Russian-annexed Crimea region.
"Our artillery has come and is being deployed against the (pro-Russian) rebels," the mayor of Mariupol, Yuri Khotlubey, told Ukraine's 112 TV channel.
As he spoke, Reuters witnesses in Mariupol heard artillery shelling a few kilometres (miles) to the east of the centre.
A commander of a Ukrainian volunteer militia based in Mariupol told Reuters by telephone that his battalion had been under sustained rebel fire all night into Friday.
"We are still keeping the rebels at bay. They are confronting us with tanks and artillery," he said.
Pro-Russian separatists told the Interfax news agency that about 50 Ukrainian soldiers had been killed or wounded in fighting near Mariupol on Thursday and three had been taken captive. The report could not be independently confirmed.
Mariupol became a major focus of concern for Ukraine after the rebels broke away from their main strongholds further north in late August - backed, Kiev says, by Russian regular forces - and took the nearby coastal town of Novoazovsk.
Representatives from Ukraine, the pro-Russian rebel leadership, Russia and Europe's OSCE security watchdog are expected to meet in the Belarussian capital Minsk later on Friday to agree a ceasefire to pave the way for implementation of a "stage-by-stage peace plan" for his country.
However, few in eastern Ukraine, wearied by nearly six months of conflict, have much hope that a ceasefire can hold.
"I would not be a decent human being if I say I am not for the ceasefire, but all these bandits and mercenaries and (Russian) invaders must be kicked out of Ukraine never to return," said Anatoly, a pensioner in his 70s, in Mariupol.
A Ukrainian soldier who gave his name as Mykola said Ukrainian President Petro Poroshenko - who was attending the second day of a NATO summit in Wales on Friday - would "betray the country" if he backed a peace plan at this time.
"If he goes for a peace plan, then all these dead and wounded and exiled and all the homes burned and jobs lost and money lost, it was all for nothing," he said.
"We must defeat them and then talk peace."