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There are credible allegations that Russia is using Wagner Group mercenaries, who've been accused of war crimes in the past, alongside its troops in Ukraine.
The Wagner Group is a private Russian mercenary force believed to be financed by an oligarch with close ties to President Vladimir Putin.
Wagner's symbol is a skull and it's named after Hitler's favourite composer.
The Group is often called "Putin's shadow army," though the Kremlin has always denied responsibility for, or even knowledge of, its activities.
And there are reports the group is fighting alongside the Russian army in Ukraine's eastern Donbas region.
The Chair of the UN Working Group on the use of Mercenaries Sorcha MacLeod told Corin Dann why she's so concerned about the group.