"About 300 men working for a Kremlin-linked Russian private military firm were either killed or injured in Syria last week, according to three sources familiar with the matter"

Reuters:

The timing of the casualties coincided with a battle on Feb. 7 near the Syrian city of Deir al-Zor where, according to U.S. officials and associates of the fighters involved, U.S.-led coalition forces attacked forces aligned with Moscow’s ally, Syrian President Bashar al-Assad.

See also:

Two Chechen-language audio recordings are circulating on WhatsApp, from a Chechen member of Wagner. He's at Hmeimim airbase and his message is "whatever you do, don't come here [to Syria]. It's not what they say. We are getting f***ing slaughtered, every day." His words.

— Neil Hauer (@NeilPHauer) February 15, 2018