The Britain-based Syrian Observatory for Human rights said today that IS fighters captured the power station and the juvenile prison just south of Hassakeh.
Hassakeh is split between government forces and Kurdish fighters who have been attacking IS positions elsewhere in the province.
IS radio station Al-Bayan said the militants are about one kilometer (mile) from the southern entrance in the city claiming to have killed dozens of soldiers.
IS has been attacking Hassakeh since May 30, facing stiff resistance from government forces.