US-led coalition air strikes on a jail run by Daesh (ISIS) in eastern Syria killed at least 57 people, the Syrian Observatory for Human Rights said on Tuesday.
"The strikes hit an IS jail in Mayadeen at dawn on Monday, killing 44 prisoners and 15 jihadists," Observatory chief Rami Abdel Rahman told AFP.
Mayadeen lies in the Euphrates Valley some 45 kilometers (28 miles) southeast of the provincial capital of Deir al-Zor.