The chief of Russian mercenary group Wagner said in a clip posted Saturday that his forces were close to the centre of the frontline hotspot of Bakhmut.
In a video posted on messaging app Telegram, Yevgeny Prigozhin is seen standing on the rooftop of a high-rise building in what is said to be Bakhmut.
"This is the building of the town administration, this is the centre of the town," Prigozhin said in the video, pointing towards a building in the distance.
"It is one kilometer and two hundred meters away," said Prigozhin, who was clad in full military gear.
Speaking as artillery boomed in the background, Prigozhin said that the most important thing was to receive more ammunition and "move forward."
Wagner has been spearheading offensives against cities in eastern Ukraine including Bakhmut, in what has become the longest and bloodiest fight of Russia's year-long assault. Both sides have suffered heavy losses around Bakhmut.
Prigozhin, an ally of President Vladimir Putin, has been entangled in a power struggle with the Defense Ministry.
He has several times claimed battlefield victories ahead of Russia's army, criticised Russia's top brass and accused the military of not sharing ammunition with his forces.
In the video released on Saturday he said he was ready to ask Russia's top commanders for forgiveness but at the same time appeared to mock Defense Minister Sergei Shoigu and Chief of the General Staff Valery Gerasimov.
He said they were "outstanding military commanders" and added that Russia's greatest military leaders including Georgy Zhukov and Alexander Suvorov "could have learnt" from them.
"I absolutely — totally — support all their initiatives," Prigozhin added.
Earlier this week Wagner said its fighters had captured the eastern part of Bakhmut.
Some military experts have questioned the sense of the continued fight for the ravaged town, but Ukrainian officials say that the fall of Bakhmut could lead to further Russian advances in the east.
The commander of Ukraine's ground forces, Oleksandr Syrsky, said Saturday the fight for Bakhmut helps win time in preparation for a future counteroffensive.
"The real heroes now are the defenders who are holding the eastern front on their shoulders, and inflicting the heaviest possible losses sparing neither themselves nor the enemy," Syrsky was quoted as saying in a statement.
"It is necessary to buy time to build reserves and launch a counteroffensive, which is not far off."
British military intelligence said on Saturday that the Bakhmutka River in the centre of Bakmut now marked the front line.
"Ukrainian forces hold the west of the town and have demolished key bridges over the river, which runs... north-south through a strip of open ground 200 meters-800 meters wide," the UK Defense Ministry said.
"This area has become a killing zone, likely making it highly challenging for Wagner forces attempting to continue their frontal assault."