Iraqis chant slogans against the Islamic State of Iraq and al-Sham as they volunteer for the army at a Baghdad recruiting station on Thursday. Associated Press
BEIRUT—The threat of Sunni extremists eclipsing the power of its Shiite-dominated Arab ally presents Iran with the biggest security and strategic challenge it has faced since the U.S.-led invasion of Iraq in 2003.
With the Islamic State of Iraq and al-Sham, an offshoot of al Qaeda, rapidly gaining territory, Iran deployed Revolutionary Guards units to Iraq, according to Iranian security officials.
Iran has invested considerable financial, political and military resources over the past decade to ensure Iraq emerged from U.S. war as a strategic partner for the Islamic Republic and a strong Shiite-led state. The so-called Shiite crescent—stretching from Iran to Iraq, Lebanon and Syria—was forged largely as a result of this effort.
Two Guards' units, dispatched from Iran's western border provinces on Wednesday, were tasked with protecting Baghdad and the holy Shiite cities of Karbala and Najaf, these security sources said.
Iraq's military was trained and equipped by the U.S. and coalition forces. When attacked by insurgents in several cities this week, Iraqi soldiers surrendered without a fight. What went wrong? What is the U.S. prepared to do? WSJ's Jason Bellini has #TheShortAnswer.
The involvement of Iran would pose yet another security challenge for the White House, and raises the prospect of the U.S. and Iran fighting on the same side. The U.S. opposes Iran's support for Syrian President Bashar al-Assad, but with Tehran is jointly supporting Iraqi Prime Minister Nouri al-Maliki.
State Department officials on Thursday refused to outline what steps the Obama administration would take if Iranian forces entered Iraq.
Spokeswoman Jen Psaki said American diplomats who met with Iranian officials in Geneva this week to discuss Tehran's nuclear program didn't raise the issue of the Iraqi crisis.
"We've encouraged them to play a constructive role in Iraq," Ms. Psaki said about the Iranians.
Iraqi Foreign Minister Hoshyar Zebari, reached by phone in London, said of the report that Iran's Revolutionary Guards were entering the fight: "Frankly I have no idea about that. I am in London now."
Syria's conflict has turned Iraq into an important operational base for Iran to aid another ally, the Assad regime, which is dominated by an offshoot of Shiite Islam. Shiite militia trained by Iran, weapons and cash have flowed from Iran to Syria via Iraq.
"Iraq is viewed as a vital priority in Iran's foreign policy in the region and they go to any length to protect this interest," said Roozbeh Miribrahimi, an independent Iran expert based in New York.
The commander of Iran's Quds Force, Maj. Gen. Qasem Solaimani, went to Baghdad this week.Shahaboddin Vajedi
Iran has also positioned troops on full alert along its border with Iraq and has given clearance to its air force to bomb ISIS rebel forces if they come within about 60 miles of Iran's border, according to an Iranian army general.
The two IRGC battalions that moved to Iraq on Wednesday were shifted from the Iranian border provinces of Urumieh and Lorestan, the Iranian security officials said.
Revolutionary Guards units that serve in Iran's border provinces are the most experienced fighters in guerrilla warfare because of separatist ethnic uprisings in those regions. IRGC commanders dispatched to Syria also often come from those provinces as well.
Iran was also considering the transfer to Iraq of Shiite volunteer troops in Syria, if the initial deployments fail to turn the tide of battle in favor of Mr. Maliki's government, the Iranian security officials said.
At stake for Iran in Iraq's current tumult isn't only the survival of a Shiite political ally in Baghdad, but the safety of Karbala and Najaf, which along with Mecca and Medina are sacred to Shiites world-wide."The more insecure and isolated Maliki becomes, the more he will need Iran. The growth of ISIS presents a serious threat to Iran. So it would not be surprising to see the Guards become more involved in Iraq," said Alireza Nader, a senior policy analyst at the Rand Corp.
A spokesman for the militant group ISIS, Abu Mohamad al-Adnani, urged the group's Sunni fighters to march toward the "filth-ridden" Karbala and "the city of polytheism" Najaf, where they would "settle their differences" with Iraq's Shiite Prime Minister Nouri al-Maliki.
Kurdish military units known as peshmerga deployed armor at the provincial capital of Kirkuk on Thursday as Iraq edged closer to full-scale sectarian conflict following lightning strikes on major cities. Agence France-Presse/Getty Images
That coarsely worded threat further vindicated Iran's view that the fight unfolding in Iraq is an existential sectarian battle between the two rival sects of Islam-Sunni and Shiite—and by default a proxy battle between their patrons Saudi Arabia and Iran.
"Until now we haven't received any requests for help from Iraq. Iraq's army is certainly capable in handling this," Iran's Foreign Ministry spokeswoman Marzieh Afgham said Wednesday.
Iranian President Hasan Rouhani cut short a religious celebration on Thursday and said he had to attend an emergency meeting of the country's National Security Council about events in Iraq.
"We, as the Islamic Republic of Iran, won't tolerate this violence and terrorism…. We will fight and battle violence and extremism and terrorism in the region and the world," he said in a speech.
ISIS's rapid territorial gains in the past few days appeared to have caught Iranian officials by surprise and opened a debate within the regime over whether Iran should publicly enter the battle.
Iran's chief of police, Esmail Ahmadi-Moghaddam said the National Security Council would consider intervening in Iraq to "protect Shiite shrines and cities," according to Iranian media.
In the short-term, analysts said the outcome of the crisis in Iraq will only strengthen and increase the influence of Iran and the Revolutionary Guards.