The Russian Defense Ministry on Wednesday confirmed that 40 service members had returned from Ukrainian captivity, in exchange for the equal number of Ukrainian prisoners. Four more Ukrainians with severe injuries were sent back as well, as a humanitarian gesture.

The Russian servicemen “faced grave danger” in captivity, the military said in a statement. They will be flown to Moscow to continue medical treatment and further rehabilitation at military facilities. All will receive the necessary mental health care as well.

Russia’s human rights commissioner Tatyana Moskalkova confirmed the addition of Ukrainian casualties to the exchange roster later in the day.

“Guided by humanitarian concerns, the Russian Defense Ministry added four seriously injured Ukrainian servicemen to the exchange, which was 40 for 40,” Moskalkova wrote.

Earlier in the day, Russia’s Investigative Committee announced an investigation into several French citizens fighting for Ukraine, accusing them of murdering Russian prisoners. According to the agency, one of the “French mercenaries” has published a photo that showed three Russian soldiers executed at point-blank range. Moscow has identified the alleged perpetrators as members of the 92nd Brigade of the Ukrainian military, as well as the infamous Azov neo-Nazi battalion.