The prospect of Iranian intervention in the Iraq crisis threatens to turn Iraq into a bloody battleground between Sunnis and Shiites.
Spurred by threats against Shia holy sites in southern Iraq, Iranian President Hassan Rouhani announced on Thursday his country was prepared to wage "combat" to repel the jihadist group known as the Islamic State of Iraq and the Levant (ISIL), which is currently sweeping across north and central Iraq.
Indeed, two battalions of the elite Quds Forces from Iran are reported by the Wall Street Journal already to have been deployed to help the Iraqi Army deal with the militant forces.
In a speech on Thursday, Mr. Rouhani drew a line in the sand. "The Islamic Republic of Iran will not tolerate this violence and we will not tolerate this terror," he said. "We will fight and combat violence, extremism, and terrorism in the region and the world."
Iran was responding to threats issued by ISIL spokesman Abu Mohammed al-Adnani, who vowed that the jihadists, who have chalked up several conquests in Iraq from Mosul to Tikrit, would not stop there but press on to Baghdad and to Najaf and Karbala, site of the two most important Shia shrines, which millions of pilgrims visit every year.
"We have a score to settle," Mr. al-Adnani said in a video statement, urging on the ISIL fighters. And the score must be settled with the Shiites.
A senior security official of Iran, a Shia state, elaborated on Mr. Rouhani's message, accusing Saudi Arabia of being behind the ISIL campaign. The Saudis, he said, are trying to take revenge in Iraq for their failure to oust President Bashar al-Assad in Syria. In an interview with the independent Al Mayadeen satellite news channel, the unnamed official said the Saudis "will feel the heat soon."
Simon Henderson, an expert on Saudi Arabia at the Washington Institute for Near East Policy, agrees with the analysis. ISIL's attack on Iraq "reflects the wider war between Shiites and Sunnis for control of the Middle East," he said.
In a paper published on Thursday, entitled The Battle for Iraq is a Saudi War on Iran, Mr. Henderson noted that ISIL's defeat of Iraqi Prime Minister Nouri al-Maliki's forces "has been the dream of Saudi Arabia's King Abdullah for years. He has regarded [al-]Maliki as little more than an Iranian stooge," refusing to send an ambassador to Baghdad and encouraging other Gulf States to do likewise.
The trouble, Mr. Henderson says, is that ISIL "is a ruthless killing machine, taking Sunni contempt for Shiites to its logical, and bloody, extreme." As such, it is very likely that Iran will be drawn in to fight it, he writes, almost certainly by deploying elements of the Revolutionary Guards, such as the Quds Force, as they were in Syria to stop ISIL and other opponents of Mr. al-Assad.
If they deploy into Iraq and take the fight into the Sunni parts of the country, analysts agree, they will ignite a sectarian civil war.
"It will be just like 2005," Michael Knights, an Iraq analyst at the Washington Institute, said in reference to the outbreak of sectarian violence during the U.S. occupation of Iraq, a conflict that killed tens of thousands.
"They will bring all the Sunnis together against the common Shia enemy," said Bill Roggio, editor of the Long War Journal in Washington.
There are signs that a lot of Iraqi Sunnis already are welcoming the jihadists. Reports on Thursday indicated that part of the reason ISIL conquered so many Iraqi towns so quickly was the friendly response it received in many Sunni communities.
Former Baathists from the time of Saddam Hussein are reported to be fighting alongside the jihadists as they drive the Shia-led Iraqi security forces from the Sunni heartland.
Some Iraqi soldiers who deserted their posts told people they had received phone calls from commanding officers ordering them to surrender.
If Iranian forces are introduced into this Sunni heartland to stop the jihadists, even more Sunnis are likely to be driven into ISIL's arms and the war will be on.
Meanwhile, Iraqi Kurds have taken action to protect their interests in the north of the country. On Thursday, the Kurds' battle-trained militia known as the Peshmerga took control of oil-rich Kirkuk. Long coveted as the Kurds' historic capital, Kirkuk also is claimed by Arab Iraqis, who insist the city and its oil fields should not be within the autonomous Kurdistan Regional Government.
Kurdish officials said that forces of the central government had abandoned the city and its surroundings and that the Peshmerga moved in only to safeguard it all.
The question is: For whom, exactly are they safeguarding it?