France, May 9 -- Human rights groups on Saturday hailed the arrest of a Ukrainian pro-Russian separatist in France on suspicion of crimes against humanity, war crimes and complicity in acts of torture.

The International Federation for Human Rights (FIDH), the Ukrainian NGO Truth Hounds, which documents and investigates war crimes, and France's Human Rights League (LDH) first told the authorities Yevhen Brazhnikov was in France four years ago.

France's National Anti-Terrorism Prosecutor's Office (PNAT) announced on Friday that the suspect, whom they only identified partially as Yevhen B., had been taken into police custody on April 7, then charged and placed in pre-trial detention.

He is suspected of having tortured detainees at the not...