FILE - In this file photo taken on Tuesday, Dec. 12, 2017, Russian President Vladimir Putin addresses the troops at the Hemeimeem air base in Syria. Several private Russian military contractors were killed by a U.S. strike in Syria, Russian media reported Tuesday, Feb. 13, 2018 in a development that could further inflame Russia-U.S. tensions if officially confirmed. (Mikhail Klimentyev/Pool Photo via AP, File)
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