Four Syrian military personnel were killed and 13 others were injured in a suspected U.S.-led airstrike in the east of the country, a monitoring group has reported.
The British-based Syrian Observatory for Human Rights said airstrikes "by the international coalition" hit a camp in the west of Deir al-Zour province sometime in the past 24 hours.
However, the U.S. has denied coalition airstrikes were the cause. U.S. Special Presidential Envoy for the Coalition to Counter ISIL Brett McGurk said on Twitter that no airstrikes had taken place near the base in Deir al-Zour.
Syria's Foreign Ministry has condemned the attacks and claimed four warplanes from the U.S.-led coalition hit the base with nine rockets, state-media agency SANA reported.
The strike destroyed three armored vehicles, four military vehicles, and a depot of arms and ammunition, the Foreign Ministry claimed.
In two identical letters addressed to the UN secretary general and the chair of the UN Security Council on Monday, Syria's government called the strike a "heinous aggression."
If confirmed, it would be the first coalition strike to have killed Syrian government forces.
"Regime forces have never previously been hit by raids from the international coalition, which was targeting jihadist bases and oil tankers in Deir al-Zour," Observatory director Rami Abdel Rahman said.
The area is largely controlled by ISIS militants who have been the target of airstrikes in the area since September 2014.
A separate strike also believed to have been carried out by coalition forces killed a woman and two of her children in the city overnight, the BBC reported.