Sputnik/Mikhail Klimentyev/Sputnik via REUTERS About 300 men working for a Kremlin-linked Russian private military firm were either killed or injured in Syria last week in a battle with the US, according to three sources. The clashes show Moscow is more deeply involved in Syria militarily than it has said, and risks being drawn into direct confrontation with the United States in Syria. The Russians reportedly were killed during a probing mission where they wanted to see if the US would respond to their advance. MOSCOW (Reuters) - 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. A Russian military doctor said around 100 had been killed, and a source who knows several of the fighters said the death toll was in excess of 80 men.See the rest of the story at Business InsiderNOW WATCH: JIM ROSS: Here's who will take over WWE after Vince McMahonSee Also:Kremlin denies Russian contractors badly defeated in Syria have any connection to Russian governmentPentagon's budget proposal has enraged Turkey, which thinks it will give $550 million to Syrian KurdsIsrael launches massive air campaign against Syria after one of its F-16s were shot downSEE ALSO: It looks like Syrian, Russian, and Iranian troops are gearing up for another fight with the US