Russia has been internationally isolated ever since Russia chose to invade Ukraine.
More of the mercenaries are gathering in Belarus, which borders several Nato members.
It comes after Poland sent troops to the border amid worries about Belarus.
The MoD claims the Wagner Group will no longer recruit Russian convicts to its ranks.
"Russia’s ‘special military operation’ has severely dislocated the Russian military training system," The MoD said.
Sviatlana Tsikhanouskaya said her children write to their father in prison.
Belarusian soldiers were previously considered "inferior" to their Russian counterparts.
Thousands of migrants are are being brutally rejected from the EU and forced to squat in woodlands instead.
Opposition leader Sviatlana Tsikhanouskaya urges PM to step up sanctions
Belarus is likely to face serious international consequences for its recent actions – but, it's unclear if they'll have any effect.