ISIS battling for 2 big prizes in Iraq

The Iraqi city of Ramadi, just 70 miles west of Baghdad, could be close to falling to Islamic State of Iraq and Syria (ISIS) militants.

CBS News correspondent Holly Williams says there are reports of fierce fighting on the outskirts of the city, and Iraq's largest oil refinery has also come under fresh attack.

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 now, 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.

Further north, just to the west of the ISIS-held town of Beiji, ISIS fighters have managed to break into the sprawling oil refinery that goes by the same name. The militants have tried for a year to penetrate the vast but well-fortified complex. Numerous attacks by ISIS have been repelled by the elite Iraqi troops stationed inside the refinery grounds.

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On Thursday, Iraqi officials conceded 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-Abadi said Iraqi forces would follow their victory in Tikrit with offensives against ISIS in Beiji and to the south in Anbar province, where 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.