The simmering standoff between the United States and Iran is feeding global concern that both countries are inching perilously close to war. It has also focused attention on Iran's network of proxy forces throughout the Middle East.
On Thursday, U.S. Secretary of State Mike Pompeo listed a series of attacks he said "Iranian surrogates" have committed since early May, describing them as part of "an unacceptable campaign of escalating tension by Iran."
Pompeo and other senior member of the Trump administration have said they will hold Tehran accountable for any attacks carried out by its allied militia forces and experts say Iran's proxies could prove potent assets for the Islamic Republic if the crisis boils over into war.
Q: Why does Iran use proxies?
A: Iran's emphasis on developing proxy forces goes back to the 1979 revolution that deposed the American-backed shah and gave rise to the Islamic Republic. The Shiite theocracy sought to export its revolution and empower Shiite groups in the Middle East from the outset. Middle East Institute Senior Fellow Alex Vatanka called this expansionist ethos "part of [Iran's] DNA."
Many - though not all - of the groups Iran sponsors are Shiite. While ideology plays a role in Iran's foreign policy, experts say the regime's primary goal is to project power throughout the Middle East to counter American, Israeli, and Saudi influence.
The success of Iran's strategy rests in large part on its ability to capitalize on power vacuums in the Middle East, Vatanka said. Most recently, Iran has broadened its reach by backing militias in war-torn Yemen and Syria amid the chaos ushered in by the Arab Spring uprisings in 2011.
How does Iran do this? Primarily through the Islamic Revolutionary Guard Corps' Quds Force, a special arm of its military focused on external operations. (The Trump administration designated the IRGC a foreign terrorist organization in April). Led by IRGC Maj. Gen. Qasem Soleimani, who answers directly to Iranian Supreme Leader Ayatollah Ali Khamenei, this branch organizes and trains fighters with allied militias and provides them with weapons, according to a recent report by the Soufan Center. Iran also uses soft power to cement economic alliances with countries like Iraq, where Iran has supported local militias in the fight against American forces in the aftermath of the 2003 invasion of Iraq and later in the battle against the Islamic State.
Q: Who are the Houthis?
A: Houthi rebels in Yemen have come under wider scrutiny since early May when they stepped up drone attacks on Saudi targets. The Houthis, who are part of the Zaydi sect of Shiite Islam, have been fighting a Saudi-led coalition in Yemen since 2015. The group had long been an opposition force in Yemen but it drew Iranian support after Saudi Arabia got involved in that nation's conflict, according to Vatanka. What began as a civil war during the Arab Spring has morphed into a proxy war between Iran and Saudi Arabia, with Iran supplying financial and military support to the Houthis and the United States providing extensive military support to Saudi Arabia.
It's unclear how much operational control Iran exercises over the Houthis, Vatanka said, but the two actors certainly share strategic priorities - namely, countering Saudi Arabia.
A spate of tit-for-tat air attacks has marked the latest escalation of the conflict between Houthi rebels and Saudi Arabia. Houthis claimed responsibility for a drone attack on a Saudi Arabia's Abha civilian airport Monday, though Saudi Arabia has yet to confirm the attack. Houthi rebels also claimed responsibility for a cruise missile attack last week that wounded 26 people on the same airport.
On Sunday, the Pentagon accused Iran of helping Houthis shoot down a U.S. drone on June 6. Saudi Arabia, meanwhile, also blamed the Houthis for attacks on two of its oil facilities.
It's unclear whether these attacks are linked to the explosions on two tankers in the Gulf of Oman last Thursday. "Is it a coincidence that it comes at the same time as intense pressure on Iran? Probably not," Vatanka said. But that doesn't necessarily mean Iran is calling the shots for the Houthis, he added.
Despite this uncertainty, Pompeo and Saudi leaders have been quick to connect Houthi-instigated attacks to Iran. In an interview with pan-Arab news outlet Asharq al-Awsat over the weekend, Saudi Crown Prince Mohamed Bin Salman accused Houthi rebels of "advancing Iran's agenda over the interests of Yemen and its people."
Houthi rebels see these strikes as self-defense against Saudi Arabia, which has been accused of indiscriminately bombing civilians in Yemen and has fueled a massive humanitarian crisis. Researcher Samuel Ramani argued that Houthi attacks on Saudi Arabian oil facilities last month were motivated primarily by the Houthis' desire to demonstrate internal cohesion and to gain popular support - rather than to serve Tehran's interests.
Q: How does Hezbollah fit into the picture?
A: Hezbollah, a Shiite paramilitary group and political party in Lebanon, is Iran's earliest and most successful proxy project. It remains the most powerful of Iran's nonstate allies in the Middle East. Formed during the Lebanese civil war in 1982, Hezbollah has since transformed from a small group of clerics and fighters into a major political force in Lebanon - with critical assistance from the IRGC.
Iran supplied weapons to Hezbollah during its 2006 war against Israel. More recently, Iran has mobilized Hezbollah's intervention on behalf of Syrian president Bashar al-Assad in Syria's bloody eight-year civil war. A U.S. Treasury Department assessment in 2018 put Iran's support for Hezbollah at $700 million per year.
Atlantic Council Senior Fellow Nicholas Blanford, an expert on Hezbollah, described the paramilitary group as "the most formidable of all the Iranian proxies in the Middle East" - and its active role in crushing the rebellion in Syria has given the group additional fighting experience.
Despite its regional military heft, few expect Hezbollah to eagerly enter into a conflict involving the United States. The group would more likely rely on low-level covert attacks on American targets in the region, Blanford said.
But, he added, "If it looks like the Islamic regime in Tehran is facing some kind of existential threat if a conflict arises, then all bets would be off."
Q: What is Iran's relationship to Iraqi militias?
A: Beginning with the Iran's war with Iraq in the 1980s, Tehran hosted and supported a number of powerful Shiite militias that were opposed to Saddam Hussein's despotic rule. After he was ousted following the American invasion of Iraq in 2003, many of those militias were marshaled to fight U.S. troops.
The Pentagon has attributed 603 American deaths in Iraq since 2003 to Iranian-backed militias. But as the Islamic State staged a lightning blitz across Iraq in 2014, those same militias became critical assets in stemming the militants' expansion and fought closely with Iraqi forces to eventually reduce the Islamic State's territorial hold to zero.
Their role in fighting the militants has given them unprecedented political power in Iraq, with many senior figures winning seats in the country's parliament last year. Their presence has given Iran additional influence over Iraq's political landscape.
U.S. officials have repeatedly urged Iraq to counter this influence.
On an unscheduled visit to Iraq in May, Pompeo warned Iraqi leaders about what he described as a growing Iranian threat in the country. "We don't want anyone interfering in their country . . . and there was complete agreement," Pompeo told reporters at the time.
In a call with Iraqi Prime Minister Adel Abdul Mahdi Thursday, Pompeo pledged the United States would help bolster Iraq's security forces. He also praised Abdul Mahdi's "continued efforts to counter threats to Iraq's sovereignty from Iran-backed militias," State Department spokesperson Morgan Ortagus said in a statement.
Meanwhile, wary of getting sucked into another war, Iraqis have been watching the escalating tensions in the Persian Gulf nervously in recent days.
Q: What role could these militias play if the conflict escalates?
A: The Trump administration has labeled Iran a "state sponsor of terror," and has sought to link Tehran to attacks carried out by allied paramilitary groups.
Some of these claims are dubious. Pompeo blamed a recent suicide bombing in Kabul on Iran, even though the Taliban had previously claimed responsibility for the attack. The Taliban and Iran do have a relationship, but experts say it is doubtful Iran was involved in the bombing.
The Trump administration's "maximum pressure" campaign is unlikely to convince Tehran to give up its support of strategic proxies like Hezbollah, Blanford said, calling American demands a "non-starter" for Iran.
As long as tensions remain confined to economic sabotage, Vatanka said, groups like Hezbollah and the Houthis will likely stay out of the fray. "Where Iran will call them in to help will be if this escalates into a conflict," he said. "How many of those will actually do something? That's an open question."
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Parker writes about foreign affairs out of The Washington Post's D.C. newsroom. She previously covered Congress for The Texas Tribune and Massachusetts state politics for The Boston Globe.