DAMASCUS, Syria - The Syrian government has accused the U.S. of leading a “brutal massacre” of its forces in Deir al-Zour province.
The U.S. has confirmed that it carried out overnight air and artillery strikes that killed an estimated 100 pro-government fighters near the Euphrates river.
The U.S. government has claimed a right to self-defence, saying it was responding to an attack on its coalition forces.
In a statement, the Pentagon said Russian mercenaries were also killed in the strikes, even though Russia subsequently denied having personnel in the area.
However, if this is confirmed, this would be the first time U.S. forces have killed Russians in Syria.
The Russian Defence Ministry has argued that it was only aware of 25 Syrian militia being wounded in the strikes, and no casualties.
The Pentagon has meanwhile argued that it had been in constant contact with Russia, raising concerns about a build-up of forces beside the SDF headquarters.
According to officials, the strikes took place in the Middle Euphrates Valley, which serves as an informal demarcation line in eastern Syria.
The government controls the western side, while the U.S.-backed Syrian Democratic Forces (SDF) control the east.
Over the past year, the two sides have clashed while trying to drive Islamic State (ISIS) militants from their last major stronghold in the country.
In its statement, the U.S. said that its forces aligned with the Syrian government crossed the agreed line and launched an "unprovoked attack" on an SDF headquarters late on Wednesday.
It further added that 500 pro-government fighters, backed by artillery, tanks, multiple-launch rocket systems and mortars, were involved in the assault.
A report featured on the Syrian news channel Al-Ikhbariyah alleged that the bombing left "dozens of dead and wounded,” and identified the pro-government fighters as "local people.”
According to the U.K.-based monitoring group, the Syrian Observatory for Human Rights, they were local tribesmen loyal to President Bashar al-Assad and Afghan Shia militiamen.
In an interview with BBC, U.S. Army Colonel Ryan Dillon, a coalition spokesperson said that Russia had assured them they were not involved, and so they felt free to launch strikes.
He added, “Everyday we communicate with our Russian counterparts so when this attack occurred they, the best way to say it is, gave us the green light.”
In a statement issued to the regional media, the Syrian foreign ministry said it had written to the United Nations, demanding international condemnation.
The ministry described the latest strikes as "a war crime and a crime against humanity,” and said the U.S. was directly supporting terrorism.
The strikes came despite the UN calling for a month-long ceasefire in the country, amid escalating violence.