Russian news reports say several private Russian military contractors have been killed by a US strike in Syria.
Kremlin spokesman Dmitry Peskov refrained from comment, saying on Tuesday that the reports needed to be verified.
Russian media said Russian private contractors were part of pro-government forces that advanced on oil fields in the eastern Deir el-Zour province and were targeted by the United States.
The US military said last week it launched air strikes on Syrian government-backed troops after as many as 500 attackers began what appeared to be a coordinated assault on Syrian opposition forces accompanied by US advisers in the province of Deir el-Zour.
It said the strikes, which reportedly killed about 100 of the attackers, were in self-defence.
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The Russian Defense Ministry said its troops weren't involved in the operation.
