Government security forces fought Thursday to regain control of the Iraq’s largest oil refinery in a decisive test of Baghdad’s ability to protect an economic pillar from Sunni Muslim insurgents. Although the battle for the refinery in Beiji, 130 miles north of the capital Baghdad, subsided early Thursday, workers in the facility’s employee housing compound said they heard mortar fire overnight. Operations at the refinery have ceased, and electricity has been cut, said Dhahi Al Jubouri, an engineer. Refinery employees said the militants had taken over most of the installation and that major gas line and two large fuel tanks had been heavily damaged in fighting between government forces and an insurgency led by the Islamic State of Iraq and al-Sham. “Gunmen are controlling some areas, and security forces are still controlling the administrative office and the production department,” Mr. Jubouri said. […]