Ukraine has rushed soldiers to the embattled eastern town of Avdiivka, surrounded on three sides by Russian forces, where the military said the situation was "extremely critical".
While the two sides staged new missile attacks on each other, Russian forces have laid siege to Avdiivka in the eastern Donetsk region since last year and its position has grown increasingly precarious in recent days.
"The Third Separate Assault Brigade confirms that it was urgently redeployed to strengthen Ukrainian troops in the Avdiivka area," the brigade said in a Telegram post.
"The situation in the town ... was extremely critical," it added.
Russian troops who have nearly encircled Avdiivka, have made progress in attempts to enter the town, with reports of street fighting in the outskirts in recent days.
Ukraine's army chief admitted Wednesday that Ukraine was outnumbered on the battlefield.
Commander-in-chief Oleksandr Syrsky described the situation as "extremely difficult" after a visit to troops around Avdiivka.
The battle for the industrial hub, less than 10 kilometres (6 miles) north of the city of Donetsk, has been one of the bloodiest of the two-year war, drawing comparisons with last year's grinding fight for Bakhmut, in which tens of thousands of soldiers were killed.
"The objective situation in Avdiivka remains threatening and unstable. The enemy continues the active rotation of troops and is throwing new forces and resources into the town," the Third Separate Assault Brigade said.
The general staff of Ukraine's army said separately that troops "continue to hold back the enemy, who keeps trying to surround Avdiivka".
It said Russia launched 34 attacks in the area on Wednesday.
Ukraine's battle to defend the city is also being hobbled by delays to much-needed Western military aid.
Almost two years after Russia invaded, Kyiv's forces are calling for Europe to deliver vital artillery shells amid shortages on the frontline.
And political wrangling in Washington over a $60-billion military aid package has raised questions over how long Ukraine's troops can hold off intense Russian attacks without the support of its key military backer.
NATO chief Jens Stoltenberg said Thursday a delay in passing new US aid for Ukraine was already hurting Kyiv's forces on the battlefield.
President Volodymyr Zelensky will travel to Berlin and Paris on Friday for meetings with Olaf Scholz and Emmanuel Macron, his office announced.
He will also meet US Vice President Kamala Harris at the Munich Security Conference on Saturday, Kyiv said.
Both countries staged new aerial attacks on targets behind the frontlines, officials said.
Russia fired 26 missiles, killing at least one person and destroying multiple homes across the country, Ukraine said.
Russia blamed a Ukrainian drone attack for a blaze at an oil depot in the western Kursk region, close to the border with Ukraine.
"Following a Ukrainian drone attack in the Kursk region, a fire has broken out in an oil depot," Regional governor Roman Starovoit said on Telegram.
Images showed firefighters tackling a large blaze in the darkness.
Kyiv has struck multiple Russian energy facilities over the winter in what it has called "fair" retribution for Moscow's own attempts to cripple Ukraine's power grid.
The Russian attacks on Ukraine killed a 66-year-old woman in the northeastern city of Chuguyiv when projectiles hit a residential area, the prosecutor's office said.
Some six people were injured in the southern Zaporizhzhia region and three in the Lviv region, hundreds of kilometres from the frontlines in the west of Ukraine.
Ukraine's air force said its air defences shot down 13 of the 26 Russian missiles.
Ukrainian police raised the death toll from strikes on the Donetsk region on Wednesday to eight. The victims included a pregnant woman and a nine-year-old child.
