The Quds Force, a U.S.-designated Foreign Terrorist Organization (FTO), has been doing the dirty work behind the scenes for Iran for decades, playing divide and conquer.

The elite paramilitary arm of Iran's Islamic Revolutionary Guard Corps (IRGC) built up an extensive network in the war-torn country, recruiting Iraqis and supporting not only Shiite militias but also Shiites allied with Washington, D.C.

The Quds Force and other elements operate covertly or sometimes openly overseas, working with Hezbollah of Lebanon, Shiite militias in Iraq and Shiites in Afghanistan.

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Ali Alfoneh, an Iranian-born scholar at the Foundation for the Defense of Democracies, cast the strategy of the Quds Force as reflecting a larger trend in Iranian society: its slow transformation from a radical Islamic theocracy to a military dictatorship, with the IRGC assuming ever greater powers.

“This is an organization [that] has engaged in spreading sectarian terror in Iraq. And now, this is the force that the Iraqi government has turned to for help in order to liberate Tikrit from Islamic State [ISIS] terrorists,” Alfoneh told Fox News in 2015. “In other words, we have one terrorist organization [that] is helping the Iraqi government get rid of another terrorist organization.”

The Quds Force reportedly has some 15,000 personnel.

President Trump ordered the game-changing U.S. military airstrike on Friday that killed the Quds Force leader, Iranian Gen. Qassim Soleimani, the Pentagon confirmed.

Soleimani is the military mastermind who was the long-running leader of the elite intelligence wing -- which itself has been a designated terror group since 2007 -- and is estimated to be 20,000 strong. Considered one of the most powerful men in Iran, he was routinely referred to as its “shadow commander” or “spymaster.”

“He is the individual most responsible for the destabilization and inflammation of sectarian tensions that Iran has sown throughout the Middle East. Soleimani is begrudgingly considered by his adversaries to be a brilliant strategist due to his pioneering of Iran’s asymmetrical warfare doctrine,” Jordan Steckler, a research analyst with opposition group United Against Nuclear Iran (UANI), said last May.

“Despite being outmanned, outgunned and outspent by its adversaries, Soleimani has employed tactics including terrorist attacks, covert operations and the outsourcing of fighting to foreign militias to undermine the sovereignty of neighboring states and expand Iran’s military and diplomatic influence," he added.

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The Quds Force was designated a Foreign Terrorist Organization (FTO) by the United States in April 2019. It was the first time the U.S. designated the arm of another government as an FTO.

The U.S. and European Union have accused the Quds Force of providing weapons and other material support to help President Bashar al-Assad suppress the uprising in Syria.

Military analysts said the IRGC began deploying fighters abroad during the Iran-Iraq War from 1980 to 1988, "exporting the ideals of the revolution throughout the Middle East."

The Quds Force emerged as the de facto external affairs branch during the corps' expansion.

In Afghanistan, the Quds Force supported the anti-Taliban Northern Alliance starting in the mid-1990s.

In 2001, it shared intelligence with the United States to topple the Taliban, reportedly prompting Soleimani to remark that "maybe it’s time to rethink our relationship with the Americans."

Relations soured in 2002, and U.S. officials have since accused the Quds Force of arming and training the Taliban, a useful tool to counter U.S. influence on Iran’s borders.

"What Quds does is very specialized, the most dangerous work, operating underground," Mahan Abedin, an Iran expert and the research director at the London-based Center for the Study of Terrorism, said in 2007.

The Quds Force -- whose name means "Jerusalem" in Farsi and Arabic -- is the most elite and covert of Iran's military branches. Over the past two decades, the corps is believed to have helped arm and train the Hezbollah guerrilla group in Lebanon, Islamic State (ISIS) fighters in Bosnia and Afghanistan, and even Sudanese troops fighting in South Sudan.

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The force is part of Iran's Revolutionary Guards, which are separate from the regular military, report directly to Iran's Supreme Leader and are tasked with protecting Iran's Islamic government.

The Quds Force, first formed in the 1980s and picked from the very best of the IRGC, is its special branch for operations outside Iran.

The Associated Press contributed to this report.