Free Syrian Army fighters are silhouetted as they stand on one of the front lines of Wadi Al-Daif camp in the southern Idlib countryside September 18, 2014. Picture taken September 18, 2014. REUTERS/Khalil Ashawi
Free Syrian Army fighters are silhouetted as they stand on one of the front lines of Wadi Al-Daif camp in the southern Idlib countryside September 18, 2014. Picture taken September 18, 2014. Reuters/Khalil Ashawi

Russian mercenaries in Syria were killed last week when US forces carried out air strikes against a pro-regime force, a US official and three Russians who have knowledge about the matter reportedly revealed. This could be the most lethal clash between the US and Russian citizens since the cold war ended if estimates of Russian casualties are confirmed.

Bloomberg reports two of the Russians as saying that over 200 contract soldiers died following a failed attack on a base held by the US and mainly Kurdish forces. Most of the soldiers were said to be Russians fighting on behalf of Syrian leader Bashar al-Assad.

The death toll, based on how the US official reportedly put it, was around a hundred. About 200 to 300 were left injured. The official, however, could not say how many casualties were Russians. Russian and Syrian officials estimated that dozens of Russians had been killed, The New York Times reports.

Twitter posts announcing the deaths were found by the Conflict Intelligence Team. “It is beyond doubt that this incident indeed took place. It is notable that the posts about their deaths emerged rather quickly – relatives and colleagues often learn of Russian mercenaries’ deaths weeks or even months after the fact,” they said in a post.

Dmitry Peskov, the spokesman for Russian president Vladimir Putin, refused to comment on reports of Russian casualties. US President Donald Trump called Putin on Monday, but Peskov reportedly said they did not talk about the military action in Syria.

Bloomberg reports Russia’s military as saying that it had nothing to do with the attack. The US reportedly accepted the claim.

On Tuesday, US Central Command said that the US forces came under fire from a tank and that they responded with strikes from drones and B-52 bombers against the attackers. The Guardian reports air force Lt Gen Jeffrey Harrigan as saying that US advisers had been in an operating base when they came under tank fire.

Harrigan added that the attacking forces were fighting on the side of Bashar al-Assad’s regime. He said he would not speculate on the composition of this force.

Defense Secretary Jim Mattis said the whole thing was “perplexing.” He gave no further details. “This is a big scandal and a reason for an acute international crisis,” Former Russian diplomat and lawmaker Vladimir Frolov said.