The Kurdish website Rudaw reported that a spokesperson for the Kurdish-led Syrian Democratic Forces, Farhad Shami, said about 1,500 Islamic State members escaped from Syria's Shaddadi prison.
Earlier, the Syrian army said "a number of" Islamic State militants had escaped a prison that had been under SDF control in the eastern city of Shaddadi, accusing the SDF of releasing them.
The army did not say how many escaped.