The Russian mercenary group Wagner claimed Wednesday to have captured the eastern bank of Bakhmut, which has seen one of the fiercest battles in the yearlong war.
The announcement came after Ukrainian President Volodymyr Zelenskyyy warned that if Bakhmut fell, Moscow would gain an "open road" for offensives deeper into the country.
Wagner chief and Kremlin ally Yevgeny Prigozhin said on social media that his forces "have taken all of the eastern part of Bakhmut," a salt-mining town with a pre-war population of 80,000.
The intense fighting around Bakhmut has been the longest and bloodiest in Russia's more than yearlong invasion, which has devastated swathes of Ukraine and displaced millions of people.
Zelenskyyy warned in an interview with CNN of what could happen if Bakhmut falls to Russian forces.
"We understand that after Bakhmut, (Russian forces) could go further" and attack nearby cities in the Donetsk region.
"They could go to Kramatorsk, they could go to Sloviansk, it would be an open road for the Russians after Bakhmut to other towns in Ukraine, in the Donetsk direction," Zelenskyy said in an interview set to air Wednesday.
Wagner has spearheaded the attack on Bakhmut and its chief, Prigozhin, is locked in a dispute with Russia's military leadership.
During a televised meeting Tuesday, Russian Defense Minister Sergei Shoigu told military officials that taking control of the city would allow for "further offensive operations" in eastern Ukraine.
Prigozhin estimated the day before that between "12,000 and 20,000" Ukrainian troops were still defending the town.
Zelenskyy told CNN that his armed forces were resolved to stay in Bakhmut.
"Of course, we have to think about the lives of our military. But we have to do whatever we can while we're getting weapons, and supplies and our army is getting ready for the counteroffensive."
Zelenskyy was set to meet U.N. chief Antonio Guterres in Kyiv as he makes his third visit to Ukraine since Russia's invasion.
Talks were expected to focus on extending a deal with Russia allowing Ukraine to export its grain.
EU defense ministers were also meeting in Stockholm to discuss a plan to rush 1 billion euros' worth of ammunition to Ukraine as pressure mounts on Kyiv's allies to bolster supplies to the war effort.
Ukraine's Western backers warn that Kyiv is facing a critical shortage of 155-millimeter howitzer shells as it fires thousands daily in its fight against the grinding Russian offensive.
During a visit to Canada on Tuesday, European Commission President Ursula von der Leyen underscored a European resolve to ward off Russian aggression.
But a report by The New York Times on Tuesday claiming that U.S. officials had seen new intelligence indicating a "pro-Ukrainian group" was behind last year's sabotage of the Nord Stream gas pipelines could raise difficult questions among the allies.
"This is not our activity," Ukraine's Defence Minister Oleksiy Reznikov told reporters in Stockholm.
As Russia said it was closer to capturing Bakhmut, Ukraine said it had identified a soldier who had gone missing in the area being shot dead in a video that sparked outrage on social media.
The footage shows what appears to be a detained Ukrainian combatant standing in a shallow trench and smoking, and then being shot after saying "Glory to Ukraine."
"Based on a preliminary examination, we believe that the video may be authentic," a spokeswoman for the U.N. Human Rights Office told AFP on Wednesday.
Both sides have said the Bakhmut battle has cost a significant number of troops, though neither has given figures.
Ukrainian officials say around 4,000 civilians, including dozens of children, remain in the town that has been virtually flattened.
