Baghdad, April 14 (IANS): The commander of a federal police force tasked with protecting Iraq's largest oil refinery was killed on Tuesday in fierce battles with the Islamic State (IS) militants who managed to seize part of the refinery, provincial security sources said.

The IS militants carried out an attack on the refinery near the town of Baiji in Salahudin province at dawn and made some progress inside the huge oil facility after heavy clashes with the security forces, killing Maj. Gen. Dhaif Khalaf and nine of his bodyguards, a source told Xinhua news agency.

The extremist militants set fire to some installations of the refinery, sending columns of black smoke above the area, and apparently prevented air support to the troops, the source said.

Despite their partial advance inside the refinery, the IS militants failed to take control of large parts of the oil facility due to the fierce resistance by the security forces, the source added.

Abdul-Wahab al-Saedi, commander of Salahudin operations, told Iraqi media that reinforcement forces arrived to Baiji, some 200 km north of Baghdad, and are moving in three directions toward the refinery in order to support the troops who are fighting inside the refinery.

The advance of IS is part of a series of attacks that targeted the oil refinery since Saturday, but the security forces reportedly repelled the attacks with the assistance of the international coalition and Iraqi aircraft.

Separately, four policemen were killed while they were trying to defuse a booby-trapped house in al-Qadsiyah district in northern part of the provincial capital city of Tikrit, some 170 km north of Baghdad, a provincial security source told Xinhua.

Meanwhile, four government-backed Sunni tribesmen were killed and two others wounded in a clash with IS militants in the village of al-Mazraa in south of Baiji, the source said.

Battles in the Sunni-dominated province of Salahudin came about two weeks after the Iraqi security forces retook control of Tikrit, when some 30,000 security members backed by allied Shia and Sunni militias and covered by Iraqi and US-led coalition aircraft launched Iraq's biggest offensive against the IS terrorist group.