It was unclear how serious Yevgeny Prigozhin was being as his fighters have proved themselves to be among Russia's most effective in Ukraine despite suffering huge losses, while any attempt by him to disengage from the war could be seen as treasonous by officials in Moscow.

"Regarding the further work of the Wagner private military company in Ukraine, I am not sure that we will work specifically in Ukraine," Prigozhin said in reply to a Danish media query.

Wagner fighters have also fought in Africa and the Middle East, where they still have some contracts.

After spearheading the months-long battle for the eastern city of Bakhmut in which tens of thousands perished, Prigozhin last month withdrew his men to rest and regroup.

Prigozhin has long been at odds with the Defence Ministry over what he says is everything from its poor leadership and tactics to ammunition shortages.

RESISTANCE

The ministry said on Saturday that Defence Minister Sergei Shoigu, someone whom Prigozhin has repeatedly vilified, had signed an order stipulating that volunteer military units should sign contracts with the ministry before July 1.

It cast the move as a step towards greater integration designed to increase the combat potential and effectiveness of such groups within the regular army and spoke of "unified approaches" to military tasks.

Prigozhin was quick to say that Wagner would not be signing any contract with the ministry despite it saying that such contracts would give volunteer groups the "necessary legal status" to operate.

The ministry has not responded to a request for comment on Prigozhin's refusal to sign up with it. It has also not publicly commented on his scathing criticism of its performance.

The Defence Ministry's Zvezda TV channel on Tuesday broadcast a report saying that three unnamed volunteer brigades and four volunteer units had signed contracts with the ministry.

Lieutenant-General Vladimir Alekseyev said after the signing ceremony that he was sure other volunteer groups would sign the same contract in the course of the next week.

The Defence Ministry said on Monday it had also signed a contract with the Akhmat group of Chechen special forces, which has often been called the private army of Ramzan Kadyrov, leader of Russia's Chechnya region.