Security forces occupying Iraq’s largest oil refinery remained besieged by fighters from the Islamic State of Iraq and Syria Saturday as American and Kurdish officials warned the garrison probably could not hold out much longer unless relieved.

About 300 Iraqi soldiers — which include about 70 members of the elite SWAT unit of the Iraqi Interior Ministry — were still in control of at least part of the huge oil refinery in Baiji after five days of fighting that has left the storage tanks of the facility on fire and fighters from the Islamic State and their Sunni Muslim tribal allies in control of at least part of the facility.

The refinery, which was evacuated of its foreign and Iraqi workers earlier in the week, produces about 60 percent of Iraq’s domestic production of refined oil products and, if it falls, would devastate Iraq’s economy, which already is forced to import hundreds of thousands of barrels of refined gasoline per day from Kuwait and Turkey. It would also offer a financial boon to the Islamic State should it get the facility even partially online as the government and consumers would likely be forced to purchase any output regardless of who it benefited. […]