The Sunni militant group that has stormed across Iraq invaded the country's largest oil refinery today, hitting it with mortars. The government is using limited air attacks to strike back at ISIS, which now controls large areas of Iraq's north.

"The oil refinery in Beiji has been under siege since the militant fighters of ISIS seized the town of Beiji in their sweep through northern Iraq," NPR's Deborah Amos reports from Irbil, Iraq. "In an offensive at dawn, ISIS fighters attacked the refinery with machine-gun fire and mortars, according to Iraqi security forces."

Amos says the facility was closed earlier this week and its German technical staff told to leave. She adds that the closure has already spurred fuel shortages, with long gas lines forming at gas stations.

Militants of the Islamic State in Iraq and Syria are now in control of 75 percent of the Beiji refinery, according to Reuters.

The news agency also says Iranian President Hassan Rouhani went on national TV last night to say the Shiite country won't allow the Sunni extremists to harm holy shrines in Iraq. And while he said that many Iranians were eager to fight in Iraq, "Thanks be to God, I'll tell the dear people of Iran that veterans and various forces — Sunnis, Shias and Kurds all over Iraq — are ready for sacrifice."

You can read about the origins of the Sunni-Shiite rift at our Parallels blog.

As we've reported, ISIS has advanced to the city of Baqouba, less than an hour's drive from Baghdad. It has already taken the large city of Mosul, along with Tikrit. Other cities are being fiercely contested.

Iraqi security forces have reportedly fought to retake parts of Tal Afar, but the country is seeking help: Its ambassador has pleaded for U.S. airstrikes, and its Shiite leader, Prime Minister Nouri al-Maliki, went on state television with Kurdish and Sunni officials to appeal for national unity.

The crisis in Iraq has prompted President Obama to meet with congressional leaders at the White House today, when they'll discuss possible ways to help Iraq's central government survive.

It's unclear what those options are. In a story Monday in which NPR's David Welna asks the question, "What, exactly, are U.S. interests in Iraq's turmoil?" he cites some experts who "question whether oil, terrorism or anything else justifies U.S. military action in Iraq."

An article at the BBC's site suggests it may be too late to help Baghdad.

"ISIS's takeover of most of the so-called Sunni Triangle, as well as Mosul, the second largest city with almost 2 million people, hammers a deadly nail in the coffin of the post-Saddam Hussein nation-building project," writes Fawaz A. Gerges of the London School of Economics. "Fragile Iraqi institutions now lie in tatters."

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