A string of explosions today rocked a munitions storage site in northeastern Syria used by the US-led coalition battling the Islamic State group, a monitor and a local official said.
"At least five explosions occurred today morning at the arms and munitions depots in a base close to Tal Tamer" northwest of the city of Hasakeh, the head of the Syrian Observatory for Human Rights, Rami Abdel Rahman said.
He said the base was used by Kurdish forces from the People's Protection Units (YPG) as well as members of the international coalition fighting IS in Syria and neighbouring Iraq.
A local Kurdish official said a number of people were injured in the blasts and loaded on to ambulances.
Neither the Observatory nor the official could specify the cause of the blasts, and the coalition was not immediately available for comment.
It was not clear if there were any US personnel on the base at the time of the blasts.
A witness told AFP that "successive explosions occurred between 10.30 am and 11 am (local time)" and said ambulances and firefighters arrived swiftly on the scene.
The US on Thursday announced the death of an American serviceman in Syria, who was killed by an improvised explosive device.
For more than two years the United States has led a 66-nation coalition using air strikes against the jihadists' positions in Syria and Iraq.
Washington has also deployed special forces in Syria to advise the Arab-Kurdish alliance, the Syrian Democratic Forces, and improve the coalition's targeting of air strikes.
As many as 300 US special forces personnel may be in Syria.