Late Sunday, Wagner Group boss Yevgeny Prigozhin posted a "report" dated May 17 that alleged Russian army soldiers had been "mining roads in the rear zone of Wagner units" in Moscow-occupied eastern Ukraine.
The report said Wagner fighters were carrying out demining operations when they came under "open artillery fire coming from positions of the defense ministry."
Prigozhin then posted a video on Telegram showing a man that he alleged was a captured Russian soldier.
"I shot at a Wagner car," the man said, adding he did so "because of a personal dislike."
The man said he was a Russian lieutenant colonel from the 72nd brigade of the armed forces.
In the video, a man who was not shown on camera was interrogating the alleged soldier, who appeared to have a bruised nose.
The video did not specify how long the alleged soldier would be held captive nor the terms for his release.
This was the first time the mercenary group said it had grabbed a soldier from the official armed forces.
Prigozhin has for months decried the state of the Russian army and accused Moscow's top generals of causing excess deaths during the Kremlin's offensive in Ukraine.
Wagner has accused the regular Russian army of not providing mercenaries with adequate ammunition.
Prigozhin has also accused the Russian defense ministry of being unable to properly defend Russia's border Belgorod region, recently intensely shelled by Ukraine.