ISIS insurgents seized a small crude oil station near the northern Iraqi city Kirkuk where 15 employees were working, security and oil officials said on Saturday.

Two officials from the state-run North Oil Co confirmed the militants seized a crude oil separation unit in Khabbaz and said 15 oil workers were missing after the company lost contact with them.

"We received a call from one of the workers saying dozens of Daesh fighters were surrounding the facility and asking workers to leave the premises. We lost contact and now the workers might be taken hostage," an engineer from the North Oil Co told Reuters, using a derogatory acronym for ISIS.

The radical movement seized at least four small oilfields when it overran large areas of northern Iraq last summer, and began selling crude oil and gasoline to finance their operations.

ISIS insurgents attacked regional Kurdish forces southwest of Kirkuk on Friday, seizing some areas including parts of the Khabbaz oilfields.

Kurdish peshmerga forces sought to push back ISIS in further fighting near Khabbaz on Saturday, Kurdish military sources said.

Khabbaz is a small oilfield 20 km (12 miles) southwest of Kirkuk with a maximum production capacity of 15,000 barrels per day. It was producing around 10,000 bpd before the attack.

ISIS has declared a medieval-style caliphate in parts of Iraq and Syria to rule over all Muslims, and it poses the biggest challenge to the stability of OPEC member Iraq since the fall of Saddam Hussein in 2003.