Russia has lost an estimated five men for every Ukrainian soldier its forces have killed in the battle for Bakhmut, according to a NATO official.
Speaking to CNN on condition of anonymity, the official said that NATO intelligence showed that Russia’s losses in the assault on the eastern town far outweighed Ukraine’s.
Despite this, the head of Russia's Wagner mercenary group said his forces had taken full control of the eastern part of the city and NATO'S Secretary General Jens Stoltenberg said it could all fall to the invading army in the next few days.
While Stoltenberg predicted the capture of Bakhmut would not be "a turning point in the war," he stressed that Russia must not be underestimated.
The battle for the city has become symbolic of the way each side has tried to wear down the other. Russian forces must go through Bakhmut in order to push deeper into the areas in Donetsk province which they are desperate to seize, but Western officials say that capturing the city won’t change the course of the war.
"What we see is that Russia is throwing more troops, more forces and what Russia lacks in quality they try to make up in quantity.
"This is now a war of attrition, which is a battle of logistics," Agence France Press quoted Stoltenberg as saying.
Ukraine has not yet commented, but president Volodymyr Zelensky has said the army is intent on defending Bakhmut and warned that Russians would have an "open road" into eastern Ukraine if the town was captured.
The Institute for the Study of War said Russian forces were likely in control in the areas cited by Prigozhin following a Ukrainian withdrawal.
Russian troops have enveloped the city from three sides, leaving only a narrow corridor leading west.
The only highway west has been targeted by Russian artillery fire, forcing Ukrainian forces defending the city to rely increasingly on country roads, which are hard to use before the muddy ground dries.
The Ukrainian military has already strengthened defensive lines west of Bakhmut to block the Russian advance, including in the nearby town of Chasiv Yar which sits on a hill.
Farther west is the heavily fortified Ukrainian strongholds of Kramatorsk and Sloviansk.
Deputy Prime minister Iryna Vereshchuk told regional media on Tuesday that fewer than 4,000 civilians, including 38 children, remained in Bakhmut. The city had an estimated prewar population of about 70,000.