Russia's Defence Ministry said on Monday it has signed a contract with the Akhmat group of Chechen special forces, a day after Russia's powerful mercenary chief Yevgeny Prigozhin refused to do so, Reuters reported.

The signing followed an order that all "volunteer units" should sign contracts by July 1 bringing them under the control of Defence Minister Sergei Shoigu, as Moscow tries to assert its control over private armies fighting on its behalf in Ukraine.

In return, volunteer fighters would get the same benefits and protections as regular troops, including support for them and their families if they are wounded or killed.

Prigozhin, who has waged a running feud with the defence ministry and accused it of failing to provide adequate ammunition supplies to his Wagner mercenaries in Ukraine, said on Sunday he would refuse to sign any such contract.

He said that Shoigu "cannot properly manage military formations".

The contract the defence ministry signed on Monday was with the Akhmat paramilitary group that has often been called the private army of Ramzan Kadyrov, leader of Russia's Chechnya region.

Unlike Prigozhin, Kadyrov has recently refrained from criticising the defence ministry. Members of the two groups have openly sparred, with one of Kadyrov's close allies on Thursday casting Prigozhin as a blogger who yells all the time about problems.

Akhmat commander Apty Alaudinov, who took part in the signing of the contract, said the unit has "prepared and sent tens of thousands of volunteers" to Ukraine in the past 15 months.

Moscow said on Friday that the Akhmat forces were waging an offensive near the town of Maryinka, in the eastern Ukrainian region of Donetsk.

"I think this is a very good thing," Alaudinov was quoted as saying by the defence ministry's website after signing the deal.

Russia's deputy chief of the general staff, Colonel General Alexei Kim, said after signing the agreement with the Chechens that he hoped other volunteer units would follow suit.

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