Russian forces on Tuesday pressed forward their weeks-long drive to encircle and capture the eastern Ukrainian city of Bakhmut where the commander of Ukraine's ground forces described the situation as "extremely tense."
The Russian troops, including mercenary fighters from the Wagner Group, are trying to cut the Ukrainian defenders' supply lines to the city, scene of some of the war's bloodiest battles, and force them to surrender or withdraw.
That would give Russia its first major prize in more than half a year and open the way to the capture of the last remaining urban centers in the Donetsk region, one of four which Moscow claims to have annexed in what it calls its "special military operation" in Ukraine.
"Despite significant losses, the enemy threw in the most prepared assault units of Wagner, who are trying to break through the defenses of our troops and surround the city," Ukraine's Colonel General Oleksandr Syrskyi said in a statement.
An unnamed soldier from Ukraine's 93rd Separate Mechanised Brigade, speaking on the Telegram messaging app as explosions boomed in the background, struck a defiant note: "February 28, the town of Bakhmut. The city is on fire, the enemy is pressing. Everything will be Ukraine..."
Russia's state-run RIA news agency released a video clip which it said showed Russian Su-25 fighter jets roaring over Bakhmut. "We are glad they are ours," says a man in the clip identified as a Wagner fighter, adding the jets helped them "psychologically."
Ukraine's military said Russia was shelling settlements around Bakhmut, which had a pre-war population of around 70,000 but now lies in ruins after months of intense trench warfare.
"Over the past day, our soldiers repelled more than 60 enemy attacks," the military said early on Tuesday, including on the villages of Yadhidne and Berkhivka just north of Bakhmut.
A Reuters reporter who visited the area on Monday said he saw no sign of Ukrainian forces withdrawing and that reinforcements were arriving despite constant Russian shelling.
Ukrainian soldiers in the Donetsk region hunkered in muddy trenches after warmer weather thawed out the frozen ground.
"Both sides stay in their positions, because as you see, spring means mud. Thus, it is impossible to move forward," said Mykola, 59, commander of a Ukrainian frontline rocket launcher battery, watching a tablet screen for coordinates to fire.
The spring thaw has a history of ruining plans by armies to attack across Ukraine and western Russia, turning roads into rivers and fields into quagmires.
Reuters saw several military vehicles stuck in mud. In a zigzag trench, Volodymyr, a 25-year-old platoon commander, said his men were prepared to operate in any weather.
"When we're given a target, that means we have to destroy it."
Russia, its forces replenished with hundreds of thousands of conscripts, has intensified its attacks right along the eastern front but its assaults have come at a high cost, Ukraine says.
Russia's defense ministry said its forces had destroyed a Ukrainian ammunition depot near Bakhmut and shot down U.S.-made rockets and Ukrainian drones.
It later accused Ukraine of launching attempted drone attacks against two southern Russian regions overnight but said they had caused no damage.
Reuters could not verify the battlefield reports.
The Russian ministry, without providing evidence, also said the United States was planning a provocation in Ukraine using toxic chemicals. There was no immediate U.S. response.
Kremlin spokesman Dmitry Peskov repeated on Tuesday Moscow's position that it is open to peace negotiations but that Kyiv and its Western allies must accept Russia's annexation of four Ukrainian regions - Donetsk, Luhansk, Kherson and Zaporizhzhia - following referendums last September Kyiv and the West says were illegal.
"There are certain realities that have already become an internal factor. I mean the new territories. The constitution of the Russian Federation exists, and cannot be ignored. Russia will never be able to compromise on this, these are important realities," Peskov told reporters.
Ukraine's outnumbered troops repelled Russia's attack aimed at taking Kyiv early in the war and later recaptured substantial territory, but Russia still occupies nearly a fifth of Ukraine.
Kyiv has so far ruled out talks with Moscow and has demanded that Russian troops withdraw to Ukraine's 1991 borders.
Separately, Russia's defense ministry said it had carried out air defense drills involving interceptor jets on Tuesday after St. Petersburg's Pulkovo Airport was forced to suspend all flights for an hour. No reason was given for the suspension, while unconfirmed media reports said an unidentified object, such as a drone, had been spotted in the area.
U.S. Treasury Secretary Janet Yellen this week became the latest senior Western official to visit Kyiv, where she announced the transfer of the first $1.25 billion from a new $9.9 billion tranche of U.S. economic and budget assistance.
Her boss, President Joe Biden, went there a week ago to mark the first anniversary of Russia's invasion of Ukraine.
"America will stand with Ukraine as long as it takes," Yellen, flanked by sandbags at the Cabinet office, told Ukrainian Prime Minister Denys Shmyhal on Monday.
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