At least 123 killed in Syria clashes

Fighting began late on Thursday with an assault by more than 100 Islamic State insurgents on the Kurdish-run Ghwayran jail in Hasakeh city, marking the group’s most significant operation since its “caliphate” was declared defeated in Syria nearly three years ago.

At least 123 people have been killed in Syria including seven civilians as battles between US-backed Kurdish forces and Islamic State group fighters raged for a fourth day, a war monitor said on Sunday.

Ongoing battles have seen IS fighters free fellow jihadists and seize weapons stored at the jail, according to the Britain-based Syrian Observatory for Human Rights, in what experts have described as a blatant regrouping attempt. In picture - Kurdish security forces deploy in Syria's northern city of Hasakeh. (AFP)

Fighting began late on Thursday with an assault by more than 100 Islamic State insurgents on the Kurdish-run Ghwayran jail in Hasakeh city - which housed the largest number of jihadists in the country -- marking the group’s most significant operation since its “caliphate” was declared defeated in Syria nearly three years ago.

The assault coincided with riots inside the prison.

Ongoing battles have seen IS fighters free fellow jihadists and seize weapons stored at the jail, according to the Britain-based Syrian Observatory for Human Rights, in what experts have described as a blatant regrouping attempt.

“At least 77 IS members and 39 Kurdish fighters, including internal security forces, prison guards and counter-terrorism forces have been killed” in violence inside and outside the prison since the start of the attack, the Observatory said.

At least seven civilians have also been killed in the fighting, according to the monitor.