US-led coalition air strikes killed almost 60 people at a Syrian prison run by the Islamic State group, a monitor said Tuesday, as Washington insisted the jihadists remain its only target.
The UK-based Syrian Observatory for Human Rights (SOHR) said the air strike took place at dawn on Monday (26 June) in the city of Mayadin, south of the embattled city of Deir al-Zour.
The prison was believed to have held a mixture of civilians and captured rebel fighters from the Free Syrian Army, reported the Deirezzor24 news website.
The worldwide coalition began its military campaign in Syria on September 23, 2014, nearly three months after the extremists proclaimed a caliphate in Syria and Iraq.
The US-led coalition said it would look into the report. It added it would assess the Observatory's allegation.
"This allegation will be provided to our civilian casualty team for assessment", he said.
Russian Federation said earlier this month that it had killed about 180 Daesh militants, including two field commanders, in June 6 and 8 air strikes on Deir Ezzor.
It was not immediately clear how either the Observatory or Deir Ezzour 24 identified the aircraft responsible for the strike.
Syrian state-run TV station al-Ikhbariya cited its correspondent in Deir al-Zor as saying coalition warplanes had destroyed a building in al-Mayadeen used as a prison by Islamic State.
As the de-facto IS capital of Raqqa has come under increasing pressure in recent days, Islamic State reportedly has moved most of its leadership to al-Mayadeen.
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