BAGHDAD -- A senior Iraqi military official with the Salahuddin Command Center said Friday that Iraqi security forces had gained full control over a contested area south of the country's largest oil refinery.

General Ayad al-Lahabi told The Associated Press that the military, backed by divisions of the Popular Mobilization Forces and coalition airstrikes, gained control Friday of the towns of al-Malha and al-Mazraah, located about 1.6 miles south of the Beiji oil refinery, killing at least 160 militants with the Islamic State of Iraq and Syria (ISIS).

Al-Lahabi said security forces were trying to secure two corridors around the refinery itself after the Sunni militants launched a large-scale attack on the complex earlier this week.

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The militants had tried for a year to penetrate the vast but well-fortified complex, and numerous attacks by ISIS had been repelled by the elite Iraqi troops stationed inside the refinery grounds.

CBS News correspondent Holly Williams reported that Iraqi officials conceded on Thursday that fighting had erupted inside the facility, and ISIS released video of clashes within the complex. Losing the Beiji refinery -- Iraq's largest -- would be a huge blow to the government and a massive symbolic victory for ISIS.

The Pentagon recently claimed that U.S.-led airstrikes and Iraqi ground forces had made significant progress against ISIS, most notably by recapturing the city of Tikrit, and retaking more than a quarter of the territory seized by ISIS in Iraq last year.

Speaking earlier this week in Washington, Iraqi Prime Minister Haider al-Abadisaid Iraqi forces would follow their victory in Tikrit with offensives against ISIS in Beiji and to the south in Anbar province, where the embattled city of Ramadi is located.

The U.S. military said coalition aircraft had carried out almost two dozen airstrikes since Tuesday targeting ISIS in Iraq and Syria, many of them concentrated around Beiji and Ramadi.

Williams said Thursday that Ramadi, just 70 miles west of Baghdad, could be close to falling to ISIS militants. There have been reports of fierce fighting on the outskirts of the city this week.

ISIS has overrun three villages close to Ramadi, according to Iraqi officials, blowing up a police station during the attack.

The militants have been battling Iraqi forces around Ramadi for several months, and large parts of the surrounding province of Anbar are already under ISIS' control. The area was a center of the al Qaeda insurgency after the U.S. invasion of Iraq in 2003.