Wagner paramilitary soldiers and members of other armed groups have been ordered to pledge allegiance to the Russian leadership as rift develops
Russian Defence Minister, Sergey Shoigu, has ordered all armed volunteers and members of the Wagner group to sign a contract with the ministry in an attempt to take direct control of the paramilitary group.
The privately-run Wagner has played a major role in the war in Ukraine but also has a significant presence in other countries.
On Monday, Russia published images of Chechen special forces Akhmat signing the agreement; angering Wagner leader, Yevgeny Prigozhin, who has pledged to boycott the contracts.
Arguments have broken out between military bosses and Wagner which has fielded tens of thousands of mercenaries in the battle for Bakhmut.
Prigozhin said: "PMC 'Wagner' is organically built into the overall system, PMC 'Wagner' coordinates its actions with the generals on the right, left, with unit commanders and has the deepest experience and is a highly effective structure.
"Unfortunately, most military units do not have such efficiency, it happens precisely because Shoigu cannot manage military formations normally."
It comes as Russian troops are reported to be suffering from low morale and shortages of ammunition.
Meanwhile, Ukraine's military said it recaptured a southeastern village, on Sunday, as Russian forces claimed to repel multiple attacks in the area.
A regional official said three people were killed when Moscow's troops opened fire at a boat evacuating people from Russian-occupied areas to Ukrainian-held territory along a flooded front line far to the south.