A White House official said on Thursday that Prigozhin had wanted to take control of salt and gypsum mines near the Ukrainian-held city in the Donetsk oblast that has been fought over by both sides for months, according to Reuters.

The U.S. has previously accused Russian mercenaries of exploiting natural resources in countries including the Central African Republic, Mali and Sudan to help fund Moscow’s war in Ukraine, although this has been rejected by Moscow.

Prigozhin said on his Telegram social media channel on Saturday that capturing Bakhmut and Soledar, which lies around 9 miles to the northeast, would be “the cherry on the cake” because of their underground network, which could be a haven for troops and tanks.

The ISW said these statements “are likely an attempt to both explain the slow pace of Wagner’s advances around Bakhmut, but may also partially explain his months-long and costly determination to establish control of the area.”

However, the think tank noted how Prigozhin was criticized by a military blogger who said that even if Soledar were seized by Russian forces, Moscow “will lose strategically due to committing their best forces to an attritional battle.”

Prigozhin is an ally of Vladimir Putin, but he has been critical of Russia’s war effort in Ukraine, without condemning the Russian president directly.

The Wagner Group has suffered high losses in Bakhmut, with an estimated 4,100 troops killed and 10,000 wounded from his force of nearly 50,000 mercenaries, according to a U.S. official cited by Reuters. This included over 1,000 killed between late November and early December.

Ukraine’s Deputy Defense Minister Hanna Maliar said on Sunday that Kyiv’s forces are fiercely defending and advancing “little by little” in parts of the Donetsk oblast, but adding “it’s very difficult in Soledar.”

A day earlier, Serhiy Cherevaty, a spokesman for Ukraine’s Eastern Group of Forces, denied Russian claims it had captured Soledar.

Meanwhile, Ukraine’s President Voldymr Zelensky said in his nightly video address on Sunday that his forces are repelling constant attacks on Bakhmut, which “is holding out against all odds” with troops also keeping their positions in Soledar.

Ukraine has also rejected Russian claims that 600 of Kyiv’s troops were killed in a “retaliatory strike” in Kramatorsk to avenge a New Year’s Eve attack on Makiivka in which Moscow said 89 troops died.

The fight for Bakhmut has been an attritional fight for both sides, which have used up a lot of artillery and manpower.

Michael Kofman, director of Russia Studies at the CNA (Center for Naval Analyses), told the War on the Rocks podcast on January 5 that while Russian forces are tasked with trying to take control of the whole of Donetsk oblast, “Bakhmut by itself as a singular axis does not offer very much.”

He said that while the only way to get to Sloviansk and Kramatorsk to secure the region was through Bakhmut, the city itself is subject to “a sunk cost fallacy.”

“The Russian military needs to take Bakhmut and the Ukrainian military need to defend Bakhmut because both sides have sunk a tremendous amount of manpower and resources into it,” he said.

While taking Bakhmut would offer Russian forces an advantage, Kofman said that they were not making any breakthroughs further south, which meant that “as tactically as it might seem relevant, strategically it is a bridge to nowhere.”

Newsweek has contacted the Russian defense ministry for comment.