An activist group and the main Kurdish militia in Syria say Kurdish fighters have besieged members of the Islamic State group in the northeastern city of Hassakeh.

Kurdish official Mustafa Bali says members of the People's Protection Units, or YPG, have cut all the roads linking Hassakeh with nearby IS strongholds in the province.

The IS group attacked several government-held southern neighborhoods in Hassakeh last month and troops have failed to retake the areas.

YPG fighters joined the battle, recently capturing several villages south of Hassakeh.

The Syrian Observatory for Human Rights and the YPG said Kurdish fighters captured a juvenile prison and a power station south of Hassakeh on Wednesday.

Before IS captured parts of Hassakeh last month, the city had been split between government and Kurdish forces.