In the latest sign of a feud between Russia's military and the Wagner private army leading its Bakhmut assault, Wagner's boss demanded more ammunition and said his aide had been barred from the military's operational headquarters.
Russia is trying to encircle Bakhmut to secure what would be its first major gain in more than half a year, at the culmination of a winter offensive that has brought the bloodiest fighting of the war.
The intense battle has depleted both sides' artillery reserves, with thousands of shells fired daily along the eastern and southern fronts.
Ukraine's European allies are working on a deal to procure more ammunition for the fight.
Ukrainian troops have been reinforcing positions west of Bakhmut in apparent preparation for a possible retreat but so far appear not to have decided to pull out.
Speaking to reporters in the Middle East, US Defense Secretary Lloyd Austin said he would not predict when or if Ukrainian troops might leave the city but that its fall "won't necessarily mean that the Russians have changed the tide of this fight".
"I think it is more of a symbolic value than it is strategic and operational value," Austin said.
Russia says capturing the city would be a step towards its major objective of seizing the full territory of the surrounding Donbas region.
Volodymyr Nazarenko, a Ukrainian commander in Bakhmut, said there had been no order to retreat and "the defence is holding," albeit in grim conditions.
"The situation in Bakhmut and around it is utter hell, as it is on the entire eastern front," Nazarenko said in a video posted on Telegram.
President Volodymyr Zelenskiy's office said he had discussed the operation on Monday with his chief of the general staff and commander of ground forces, who both "spoke in favour of continuing the defensive operation and further strengthening positions in Bakhmut".
Yevgeny Prigozhin, the Wagner boss who sent tens of thousands of convicts recruited from Russian prisons into battle around Bakhmut, issued the latest in a barrage of statements that have deepened his rift with Russia's top brass.
Prigozhin said he had written a letter on Sunday to the commander of the Ukraine campaign "about the urgent need to allocate ammunition".
On Monday morning he said his representative at operational headquarters had his pass cancelled and had been denied access.
Since the start of this year, the Ukraine campaign has been commanded personally by Russia's top general, Chief of the General Staff Valery Gerasimov.
Prigozhin claimed last week that his men had practically surrounded Bakhmut.
But on Saturday he appeared in a video with a gloomier assessment, warning that the front would collapse should Wagner be forced to retreat - although it was not clear when the video was recorded.
He has accused ministry officials of "treason" for failing to supply adequate ammunition to his forces, something the ministry has denied.
A spokesman for Ukraine's 10th assault brigade, Mykyta Shandyba, told Ukrainian television "it was clear" Russian forces faced a shortage of ammunition that had limited their advances in Bakhmut.
However, he said Russia's attacks had intensified in recent days, with groups of 30 people trying to break through Ukrainian defence lines.
"They failed so far," he said.
Russian Defence Minister Sergei Shoigu, who has kept a low profile for most of the war, has been on a rare visit to his forces in Ukraine in recent days, awarding medals and meeting commanders.
On Monday, he visited the eastern city of Mariupol, largely destroyed by Russian forces last year after a months-long siege.
