The situation on Ukraine's eastern front lines is getting tough, President Volodymyr Zelensky has said.
Ukrainian troops are facing a very difficult situation in three heavily contested towns in Donetsk - Bakhmut, Vuhledar and Lyman - Mr Zelensky said.
The UK's defence ministry said Ukrainian soldiers are becoming isolated in embattled Bakhmut.
The head of Russia's notorious Wagner group said there are fierce battles for every street in some areas of the town.
Russian forces have been attempting to seize control of Bakhmut for months - making it the longest battle since Russia invaded Ukraine almost a year ago.
Taking the area is important to Russia in furthering its aim of controlling the whole of the Donbas region in the country's east. It would also signify a turnaround in Russia's fortunes after it lost ground in Ukraine during recent months.
Despite the flow of Western weapons to Ukraine, Russia has made gains around the Bakhmut area in recent days, as Russia's army throws more and more soldiers into combat.
Speaking during his nightly address, President Zelensky said: "During the 346 days of this war, I often had to say that the situation at the front was tough. And that the situation is getting tougher.
"Now is that time again. A time when the occupier throws more and more of its forces to break our defences."
The UK's Ministry of Defence said Ukrainian forces in Bakhmut are getting increasingly isolated as the Russians continue to make small advances in its attempt to encircle the town.
It added that the two main roads into Bakhmut were likely being threatened by direct fire.
Russia's paramilitary mercenary group Wagner have led much of the fighting in the area
The head of the force, Yevgeny Prigozhin, confirmed that there are "fierce battles for every street, every house, every stairwell" in northern parts of Bakhmut.
Responding to reports that Ukrainian forces had retreated from the town, he said this is not the case and Ukrainian soldiers are "fighting to the last".
The battles on the front line come as more missiles hit parts of eastern Ukraine.
In the north-eastern city of Kharkiv, five people were wounded after strikes hit civilian buildings in the city, the head of the Kharkiv regional administration Oleg Sinegubov said.
Five others were injured in the Donetsk region during rocket attacks, Pavlo Kyrylenko, head of Donetsk's regional administration said.
Four others were killed in the Donetsk region a day earlier, he said.
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