The prisoners are people who have been jailed by the IS. (Representative image) Photograph: (Reuters)
42 prisoners and 15 jihadists have been killed, according to Syrian Observatory for Human Rights chief Rami Abdel Rahman
57 are dead after a US-led airstrike targeted a jail run by the Islamic State (IS), AFP reports, citing the Syrian Observatory for Human Rights.
The prisoners are people who have been jailed by the IS, not IS members who have been imprisoned.
"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 kilometres (28 miles) southeast of the provincial capital of Deir Ezzor.
Earlier today US General Jim Mattis said that America did not want to enter the Syrian civil war, a comment made in response to President Trump's vague threat that if Syria's Assad used chemical weapons against his population, Assad would "pay a heavy price".