The head of Russia's Wagner private army has said it is not getting the ammunition it needs from Moscow, as it seeks to gain control of Bakhmut.
Russian troops - from Wagner and regular Russian forces - are trying to seize the eastern city from Ukraine.
But Wagner boss Yevgeny Prigozhin has complained of a lack of ammunition, saying it could be "ordinary bureaucracy or a betrayal".
Relations between Wagner and Moscow seem increasingly tense.
The Wagner group has tens of thousands of troops in Ukraine -
some recruited directly from Russian prisons - and has become a key part of Moscow's invasion.
In the post on Sunday, Mr Prigozhin said documents were signed on 22 February, with ammunition expected to be sent to Bakhmut the next day.
But most has not been shipped, he said, before suggesting it could be deliberate.
Separately, in a video posted on Saturday - but seemingly filmed in February - Mr Prigozhin said Russia's front line would collapse without his troops.
"If now Wagner PMC [private military company] retreats from Bakhmut, then the entire front will crumble, and today PMC Wagner is cementing it.
"On the one hand, we are pulling the entire Ukrainian army onto ourselves, grinding and destroying it, and do not give it the opportunity to concentrate in other sectors of the front.
"On the other hand, we are moving forward and the rest [an apparent reference to the Russian military] are forced to somehow catch up in order to save face."