Ukrainian President Volodymyr Zelenskiy this week described the pressure his armed forces were under in the Donbas region in eastern Ukraine as "hell".Â
He spoke of fierce fighting around the town of Avdiivka and the fortified village of Pisky, where Kyiv has acknowledged its Russian foe's "partial success" in recent days.
The Ukrainian military said on Thursday Russian forces had mounted at least two assaults on Pisky but defenders had managed to repel them.
Ukraine has spent the last eight years fortifying defensive positions in Pisky, viewing it as a buffer zone against Russian-backed forces who control the city of Donetsk about 10km to the southeast.
The Russian defence ministry on Thursday confirmed its forces were on the offensive.
It said they had inflicted heavy losses on Ukrainian forces around Avdiivka and two other locations in Donetsk province, forcing Kyiv's mechanised infantry units to withdraw.
Video footage released by the Russian defence ministry showed Russian rocket launchers in action and tanks advancing and firing at speed across open terrain. It was not clear where they were filmed.
Some unverified reports suggest Russian-backed forces have reached Pisky's outskirts.
Supplied with sophisticated arms by the West, Ukraine has been targeting Russian-backed forces in the area.
Officials in the self-proclaimed Donetsk People's Republic said on Thursday Ukrainian shelling had killed at least five people and wounded six in Donetsk city.
Footage on social media showed bodies, some blown apart, lying beside a road in central Donetsk. Blood stained the pavement.
Pavlo Kyrylenko, the Ukrainian governor of Donetsk, said on Telegram three civilians had been killed by Russian shelling in Bakhmut, Maryinka and Shevchenko.
Eight people had been killed and four wounded by Russian artillery shelling in the town of Toretsk in Donetsk, he said.
Russia denies deliberately targeting civilians.
Ukraine and the West, who describe Russia's actions as an unprovoked imperial-style war of aggression, say Russian forces must withdraw to their positions of pre-February 24 when President Vladimir Putin sent tens of thousands of troops into Ukraine.
Moscow, which regularly talks of the need for its forces to advance deeper into Ukraine, looks unlikely to agree to do that voluntarily.
Ukraine said the Russian offensive in the east looked like an attempt to divert troops from the south where Kyiv's forces are trying to retake territory and destroy Russian supply lines as a prelude to a wider counter-offensive.
"The idea is to put military pressure on us in Kharkiv, Donetsk and Luhansk over the next few weeks. What is happening in the east is not what will determine the outcome of the war," Ukrainian Presidential adviser Oleksiy Arestovych said in an interview on YouTube.
NATO Secretary-General Jens Stoltenberg said on Thursday the war was the most dangerous moment for Europe since World War II, and Russia must not be allowed to win it.
To prevent Moscow from succeeding, NATO and its member countries may have to support Ukraine with arms and other assistance for a long time to come, he said.
"It's in our interest that this type of aggressive policy does not succeed," Stoltenberg said in a speech in his native Norway.
Amid fears among some politicians in the West that Russia's ambitions may extend beyond Ukraine, Stoltenberg warned Putin the response to such a move from the Western military alliance would be overwhelming.
"If President Putin even thinks of doing something similar to a NATO country as he has done to Georgia, Moldova or Ukraine, then all of NATO will be involved immediately," Stoltenberg said.
The war has led previously non-aligned Finland and Sweden to seek NATO membership, with the request so far ratified by 23 of the 30 member states.
Russia, which shares a long land border with Finland, has repeatedly warned Finland and Sweden against joining NATO.
