As the United States and Iran trade threats and risk a potential collision, the Trump administration is struggling to counter Tehran’s network of proxies across the Middle East. The sprawling network is armed not only with missiles and mines, but also with political influence.

Earlier this month, U.S. officials said intelligence indicated Tehran had given a green light to its proxies in the region to go after U.S. targets. That prompted the White House to issue stern warnings to Iran, beef up U.S. forces in the Persian Gulf, and order a partial evacuation of American diplomatic missions in Iraq.

A still unexplained attack on four ships in the Persian Gulf, along with a drone attack on a pipeline in Saudi Arabia claimed by Houthi rebels, has fueled tensions and underscored the dilemma Washington faces in confronting a regime that can strike back through its partners without leaving clear fingerprints. Iran has denied any role in the attacks.

If the war of words erupts into a full-blown conflict, the U.S. military would have to contend with Iran’s network of armed militias in the region. Despite its relatively modest military might, Iran has long employed proxies to fend off adversaries and extend its power and political influence.

“The U.S. can destroy the Iranian navy in a day, but it will find it is attacked in six countries by proxy networks,” said Michael Knights, a senior fellow at The Washington Institute think tank.

At relatively low cost and low risk, local Shiite allies armed and trained by Iran have over decades inflicted serious casualties and strategic headaches on its enemies, including Israel and the United States.

The administration of President Donald Trump has warned that it will retaliate directly against Iran if its surrogates target U.S. troops or civilians.

But Iran denies it is seeking a war with the U.S. and has accused the Trump administration of intentionally stoking tensions.

For Tehran, proxies from the Mediterranean Sea to the Gulf of Oman provide an extended defense far beyond its borders, making adversaries think twice before launching an attack on Iran.

Since the 1980s, Tehran has gambled successfully that its rivals will not directly target its territory, and instead hit back only at the local forces it arms and trains.

Last week, Saudi Arabia blamed Iran and its Houthi allies in Yemen for a drone attack on an oil pipeline pumping station. But Riyadh responded by targeting Houthi forces in Yemen, not by carrying out strikes on Iran itself.

Houthi forces launched another drone attack on Saudi Arabia on Tuesday, going after hangars at Najran airport, the rebels’ television network reported.

Attacks carried out by Iran’s local allies complicate Washington’s decision-making calculus. Would Trump be prepared to go to war with Iran over an incident in which a proxy was suspected? What if the intelligence was circumstantial and left open the possibility Iran did not order the attack by the proxy force?

The value of proxies

While it has armed and trained militias that have carried out large-scale violence, Tehran’s approach to local partners has a nuanced political element as well, experts said. In Lebanon and Iraq, the regime’s proxies have steadily amassed political weight, pushing those countries into Iran’s orbit.

Iran’s playbook starts with arming mostly Shiite groups that evolve “into political movements that acquire political legitimacy, seats in national parliaments and cabinets, and, over time, major roles as national decision makers,” according to a recent report by the Soufan Group, a global security firm that tracks developments in the Middle East.

“Iran essentially seeks to nurture its allies and proxies to the point where they, and by extension Iran, can take over state power from within.”

In 1983, a group linked to the Iranian-backed Shiite militia Hezbollah claimed responsibility for lethal bombings of the U.S. embassy in Beirut and a U.S. Marine barracks. Months later, President Ronald Reagan pulled American troops out of Lebanon.

During the U.S. war in Iraq, Iranian-linked Shiite militia hit American forces with especially lethal roadside bombs that could penetrate armored vehicles. The Pentagon says those attacks killed hundreds of U.S. troops between 2003-2010. Sixteen years since the U.S. invasion of Iraq, those militia groups wield significant influence in the country.

In Syria’s civil war, tens of thousands of Hezbollah fighters and Iranian-trained Shiite militia — backed by Russian air power — shored up the regime of Bashar al-Assad, pushing back fighters backed by Turkey, Saudi Arabia and other Arab governments.

In the civil war in Yemen, Iranian-backed Houthi rebels have launched missiles and rockets into Saudi Arabia and fought a coalition led by Riyadh to a stalemate on the battlefield since 2015.

Iran first discovered the value of proxies in its eight-year war with Iraq in the 1980s, when Iraqi Shiite fighters proved effective against Saddam Hussein’s regime.

Supporters of the Houthi movement shout slogans as they attend a rally to mark the 4th anniversary of the Saudi-led military intervention in Yemen's war, in Sanaa, Yemen on March 26, 2019. Khaled Abdullah / Reuters

An arm of Iran’s Revolutionary Guard Corps, the Quds Forces, runs the training efforts for various proxies, and Hezbollah in Lebanon has grown into that country’s most powerful political and military force.

By operating covertly through partners who don’t wear Iranian military uniforms, Tehran can deny its involvement, experts said.

“When Iran’s proxies carry out attacks, it’s highly implausible that they don’t coordinate with Tehran, but it’s usually not provable,” said Karim Sadjadpour, a senior fellow at the Carnegie Endowment for International Peace.

In Lebanon, Iraq, Syria and Yemen, Iran has exploited the chaos of civil wars, enabling it to promote its interests and keep its rivals off-balance.

“It is relatively cheap to equip militias, some of whom already believe in the cause and are willing to fight and die,” said Behnam Ben Taleblu of the Foundation for Defense of Democracies think tank, which supports a tough line on Iran.

“The strategy is low cost but with a high return on investment.”

Iran’s tactics, however, have antagonized Gulf Arab powers, particularly Saudi Arabia. The Shiite-ruled regime in Tehran has aspired to be the leader of the Islamic world, but its efforts to rally Sunni Muslims have had mixed success.

Expanding forces

Trump administration officials say a wave of punishing U.S. economic sanctions will deprive Iran of funds for its Shiite militias and force the regime to scale back its role in Syria, Iraq and Yemen. The sanctions, which have drastically slashed Iran’s oil revenue, reportedly have forced Hezbollah to adopt austerity measures, furloughing fighters and cutting staff at its television station.

But so far, ramped up U.S. economic pressure has yet to cause Iran to pull back on its proxy activity across the region, according to Seth Jones of the Center for Strategic and International Studies think tank.

Iran’s proxy forces have expanded since 2011, according to a recent report by Jones. The number of fighters in Iran’s proxy network has increased from roughly between 110,000 and 130,000 in 2011 to between 140,000 and 180,000 in 2018, the report estimated.

Iran’s partners also are using increasingly advanced weapons, including long-range rockets, armed drones, explosive-laden speed boats and Iranian-made Burkan 2-H medium-range ballistic missiles, according to Jones and United Nations experts.

Some regional analysts and former intelligence officials say Iran’s proxy war with the U.S. could already be underway.

Houthi rebels claimed responsibility for a drone attack last week on Saudi Arabia’s East-West pipeline, which takes Saudi crude from the Persian Gulf across the country to the Red Sea in the west.

Days earlier, four ships — including two Saudi tankers — came under attack off the coast of the United Arab Emirates, near the oil export port of Fujairah. It remains unclear who was behind the assault. U.S. officials say Iran and its proxies are the prime suspects — though they have yet to provide proof.

Iran has denied any role in the attacks on the ships or on the oil pipeline.

The attacks, which caused no fatalities and did not directly target the U.S., could be an attempt by Iran to send a warning to Washington that it has the ability to send oil prices soaring and disrupt oil shipping lanes not only in the Strait of Hormuz, but outside of the strategic waterway, Knights of the Washington Institute said. Both incidents took place at key hubs for oil routes bypassing the narrow strait.

Knights said the attacks sent a clear message: "You already know we can touch Hormuz. Here’s the other two things that you are counting on for getting your oil out. We can touch them too."