WASHINGTON -- The Pentagon says U.S. military commanders were told by their Russian counterparts that there were no Russians in a paramilitary force whose attack on a base in eastern Syria earlier this month led to a massive counterstrike by U.S. forces.
The comments by Defense Department spokeswoman Dana White on February 22 add another piece to the puzzle surrounding the February 7 incident, which Moscow said this week caused dozens of casualties among fighters from Russia and other former Soviet republics but did not involve uniformed Russian troops.
Defense Secretary Jim Mattis and other U.S. military officials have repeatedly said that U.S. military commanders were in contact with their Russian counterparts at the time of the clash. But White's comments are the clearest to date that the U.S. military was told there were no Russians in the attacking force.
"The strike in Syria -- our strikes were done out of self-defense. We were very clear about that. We saw those -- that group moving towards us. We still don't know, and I won't speculate, about the intentions or the composition of that group," White said.
"What I can tell you is that we used our deconfliction phone line, and we used it before, during, and after the strike. And we were assured by the Russians that there were no Russians involved," she said.
The clash in Deir al-Zor Province appears to be the first time that U.S. forces engaged directly with Russians in Syria, where Russian forces are backing President Bashar al-Assad's government in a devastating seven-year civil war.
The revelation that Russian mercenaries were killed stoked fears of an outright hostile confrontation between Russians and U.S. forces. But the Russian government has distanced itself from the incident and its public comments have been subdued.
The United States has said that air and artillery strikes launched after as many as 500 pro-government forces attacked a base housing U.S.-backed opposition forces and U.S. military advisers killed about 100 of the attackers.
No Russian official directly acknowledged that Russian citizens were involved until February 15, when Foreign Ministry spokeswoman Maria Zakharova said that about five people who were "presumably Russian citizens" may have been killed.
On February 20, the Russian Foreign Ministry said "several dozen" citizens of Russia and other former Soviet republics were wounded in the lopsided exchange.
With accounts from relatives and acquaintances of Russian fighters in Syria mounting, some open-source researchers and media reports have said that dozens or hundreds of Russians were killed.
Russia has given Assad's government crucial support throughout the war in Syria, which began with a government crackdown on protests.
Moscow helped turn the tide of the conflict in his favor by launching a campaign of air strikes in 2015 and stepping up its military presence on the ground.
In Russia, anger is growing among relatives of the dead and survivors, and supporters of private military companies like Vagner, which is believed to have sent hundreds of contract soldiers to Syria.
The company is financed by a wealthy St. Petersburg businessman, Yevgeny Prigozhin, who is known for his close ties to the Kremlin.
Some relatives have said their loved ones were lured by the company's relatively high wages, but were deceived into thinking they were going to work on construction projects.