Former Russian commander Igor Girkin warned on Saturday that Russian President Vladimir Putin might face “military mutiny” from the Wagner Group, a private military unit whose leader Yevgeny Prigozhin reportedly threatened to withdraw his troops from Bakhmut.

On Saturday, Girkin wrote in a Telegram post that calling for the withdrawal of units from “the front without the consent of the high command is a military rebellion and nothing else.”

The Wagner Group has played a key role in helping Russian forces in their attempt to take control of Bakhmut in Ukraine. Still, Prigozhin has often publicly criticized the Russian defense ministry for not providing his fighters with more ammunition and support.

In another Telegram post on Saturday, Girkin wrote that Prigozhin “openly” blackmailed Russia’s military leadership by warning that the Wagner Group would leave its position in Bakhmut if the issue of supplying his forces with ammunition wasn’t resolved by Friday.

The former Russian commander also wrote that Prigozhin is aware that withdrawing his troops could lead to “catastrophic consequences” for Russia ahead of Ukraine’s counteroffensive, which is expected this spring. The West, including the United States, has been supplying Ukrainian troops with advanced military equipment, tanks, and artillery, among other resources, to help the war-torn country be well-prepared for its upcoming counteroffensive.

Girkin added that Prigozhin warned of withdrawing his troops in a letter sent to Russian Defense Minister Sergei Shoigu. Newsweek was unable to verify whether or not Prigozhin issued this warning to Shoigu or whether the mercenary group is suffering from an ammunition shortage. However, Reuters reported on Friday that Prigozhin said that his forces are suffering heavy casualties because Putin’s regime is not supporting his group.

The Wagner leader also said this week he was joking when he stated that his troops would stop attacking Bakhmut to allow Ukrainian troops to show the city to American journalists, according to Reuters.

Meanwhile, Girkin wrote on Saturday that Prigozhin previously “spoke extremely badly of both the Russian command and the Russian army as a whole, [saying] ‘we must forget the word Airborne Forces are doing something in Bakhmut.'”

Girkin has been an avid critic of Prigozhin and the Russian defense ministry over the country’s operations in Ukraine. Last month, he said that removing Prigozhin was “urgently necessary.”

“Since his political ambitions (multiplied by psychopathy, the organization’s demonstrative war crimes, a tendency to shamelessly and in many respects falsely self-promote and spread rotten ‘criminal concepts’ to the armed forces)—only harm both Wagner and the common cause of victory over ‘Ukraine,'” Girkin wrote on Telegram at the time.

He also said that the paramilitary mercenary, along with Russian troops, need to be withdrawn from the frontlines “for replenishment and reorganization, in order to subsequently be used in a more promising strategic direction to break through the front.”

Newsweek reached out by email to the Russian defense ministry for comment.