The US has intervened to help Iraq hold its most important oil facility

The US military has started running supply flights to support Iraqi security forces holding the huge, vital oil facility at Baiji.

The refinery, the largest in the country, is surrounded by ISIS fighters and their supporters. It's been shut down since mid-June, but the government is still clinging to control. A force of several hundred Iraqi troops and government supporters inside the refinery has fought off numerous attacks by insurgents over the past four months.

Ben Lando, editor of the Iraq Oil Report, says his sources report that the Iraqi government stopped running its own supply flights to the refinery after ISIS, which also calls itself the Islamic State, shot down at least two Iraqi helicopters in recent weeks.

"It seems that the Islamic State militants have been able to get their hands on some particularly effective anti-aircraft rocket launchers. And that has had a major toll," he says.

The US has expanded its own air operations in response, Lando says, conducting resupply drops and bombing ISIS positions around the refinery. He says US advisers are also providing intelligence to Iraqi forces, who are working to retake the territory around the refinery. Iraqi forces, he says, are "making their way, village by village, taking it back."

"Neither side can actually operate the refinery unless they have both control of the refinery itself and the surrounding area," he explains, "because it's not a stand-alone piece of infrastructure. It requires the fields to be able to deliver the oil to it, and it requires the ability to send fuel back out, whether it's by pipeline or by tanker truck."

But Lando says an all-out fight to take the refinery remains unlikely; neither side wants to damage the valuable installation. And, of course, there are the persistent coordination problems that plague the Iraqi military.

"All of that requires everybody to be on the same page," he says. "And, as we know, that's not the case."