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."
Meanwhile, Britain's Foreign Secretary Philip Hammond said the West would push ahead with sanctions against Russia over the crisis in Ukraine but said these could be lifted should a proposed ceasefire take hold.
Hammond also told BBC TV that Britain had made no commitment to take part in any air strikes against Islamic State jihadists in Iraq, but was still considering the possibility of military action.
"Our economies are fundamentally more robust and resilient than the Russian economy and if Russia ends up in an economic war with the West, Russia will lose."
However, he said measures against Russia could be eased if a proposed ceasefire between Ukraine and pro-Russian rebels expected to be agreed later on Friday takes hold.
"If there is a ceasefire, if it is signed and if it is then implemented, we can then look at lifting sanctions off but ... there is a great degree of scepticism about whether this action will materialise, whether the ceasefire will be real," Hammond told BBC TV.
"We can always take the sanctions off afterwards, I don't think we want to be distracted from our determination to impose further sanctions in response to Russia's major military adventure into Ukraine."
Hammond also said Britain had made no commitment to take part in any air strikes against Islamic State jihadists in Iraq, but was still considering the possibility of military action.
"The U.S. is already carrying out air strikes, we in Britain have made no commitment to take part in any air strikes as yet but we will certainly consider that possibility if we think that it is the best and most effective way to support a credible and inclusive Iraqi government when one is formed."