A U.S. strike in Syria reportedly killed an unknown number of Russian private contractors, according to Russian media.
Neither Russian nor U.S. officials have said much about the incident, which could complicate or intensify strained relations between the two nations, if indeed Russian forces were killed while attempting a direct attack on U.S. forces, ABC News reported.
The Russian Defense Ministry said 25 Syrian volunteers were wounded.
Unconfirmed claims cited in Russian media report 200 casualties, a majority of which are Russian.
The Tass news agency reported two Russian citizens as having been killed in Syria, and the Interfax news agency reported two other Russians killed in combat.