Sunni rebels are still in control of Iraq’s Baiji oil refinery, workers say, a day after insurgents reportedly beat back the Iraqi government troops who originally defended the facility.

Clashes between the Islamic State of Iraq and Syria (ISIS) and Iraq’s counterterrorism units were expected to multiply on Thursday after a day of assaults that heavily damaged a major gas line and two large fuel tanks, the Wall Street Journal reported.

The refinery in Baiji, located 130 miles north of the capital, Baghdad, is the largest in Iraq and the main source of fuel for the domestic market. The Sunni takeover has prompted fears of major supply shortages in Iraq and across the region, which in turn triggered a spike in global oil prices.

ISIS forced the refinery to shut down and cut its electricity earlier this week, and on Wednesday the militants took over three-fourths of the refinery, though which parts the rebels control is disputed by both sides.

An official inside the refinery told the media yesterday that the production units, administration building and four watch towers were all under ISIS control. An engineer at the plant told the WSJ that while gunmen are controlling some areas, Iraqi security forces are still protecting the administrative office and production department.

An Iraqi military spokesman, Gen. Qassim Attam, has denied that insurgents overtook the refinery at all and said on Wednesday that it remained under full government control, the WSJ said.

Brent crude, an oil price benchmark, rose above $114 a barrel to a nine-month high as investors worried increasingly about oil exports from Iraq, Reuters reported.

Iraqi officials said the major oilfields in the southern parts of Iraq are still safe from the armed insurgency, but foreign oil companies have started pulling foreign staff out of the country amid fears that the violence could engulf the entire nation.