Asked about whether there were any Russian mercenary deaths at a Senate Intelligence Committee hearing on February 13, CIA Director Mike Pompeo said, without elaborating: "From an intelligence perspective, we have seen in multiple instances foreign forces using mercenaries in battles that will begin to approach the United States".
The Pentagon says it is in constant contact with Russian forces on the ground as part of an existing de-confliction agreement that had been agreed between Washington and Moscow. Moscow's defense ministry issued a statement denying the involvement of any Russian service members.
Reuters reported the names of at least two Russian men fighting informally with pro-Assad forces who were killed in the incident in Deir al-Zor province, citing interviews with their associates. Because of Russia's formal support for Assad's regime, combined with a history of misrepresenting Russian troops as mercenaries when the Kremlin wants to avoid being implicated in military action, have led many to postulate that the troops killed or wounded in the assault across the Euphrates river last week, as well as the crew of the T-72 destroyed on Saturday, may indeed have been Russian, rather than militia fighters.
Yury Barmin, a Middle East analyst at the Russian International Affairs Council, a think tank set up by the Kremlin, said Russia supports Assad's efforts to reclaim the "crucial" eastern region of Deir Ezzor to help fund his national reconstruction and reconciliation plan, which the USA opposes. Mercenaries, who've been active in the conflicts in eastern Ukraine and Syria, allow Russian Federation to deny official involvement in operations when things go wrong.
Maksim Buga, a leader of the Cossack community in Kaliningrad, told AFP that "our Cossacks are there [in Syria] as part of a volunteer group".
Mattis, speaking to reporters Tuesday while traveling in Europe, said he had seen news reports of Russian contractors being killed in that fighting, which he described last week as a surprising assault in light of obvious US advantages, including overwhelming air power.
The Syrian government had previously said it would welcome the results of the Sochi congress, but Soussan's statement makes it seem unlikely, leaving the peace process with no certain future.
The Syrian Observatory for Human Rights says the shell landed near the hospital entrance.
Escalated attacks on Eastern Ghouta coincide with a surge in violence in other parts of the country, including the opposition stronghold of Idlib and the Kurdish enclave of Afrin.
Assad's government in Damascus called the us military action "barbaric" and a "war crime".
"The call for an immediate cessation of hostilities ... has gone unanswered", al-Za'tari said.
The two sides have clashed over the past year while trying to drive Islamic State (IS) militants from their last major stronghold in the country.
Bloomberg reported Russia's military as saying that it had nothing to do with the attack. Russia, Iran, Israel and Turkey have all had aircraft shot down in or near Syria this month. Separately, the U.S.is supporting a group of Syrian Kurds and Arabs, dubbed the Syrian Democratic Forces, fighting the Islamic State.
Turkey is conducting a cross-border operation in the enclave to rout a US -backed Syrian Kurdish militia that Ankara considers to be a "terrorist" group.