Mourners carry the coffins of Iran-backed Popular Mobilization fighters killed in a U.S. airstrike in Qaim, during their…
Mourners carry the coffins of Iran-backed Popular Mobilization Forces fighters killed in a U.S. airstrike in Qaim, during their funeral in Najaf, Iraq, Dec. 31, 2019.

The hundreds of Iraqi Shiite protesters and militiamen who tried to storm into the U.S. embassy in Baghdad on Tuesday were led by a powerful pro-Iran militant group Kataeb Hezbollah.

Kataeb Hezbollah commander Abu Mahdi al-Muhandis joined the attackers as they torched a security post and hurled stones at the U.S. compound, enraged by U.S. airstrikes in Iraq and Syria that killed at least 25 members of the group on Sunday.

Here is a look at the history and facts of the Iranian-backed Iraqi group:

'Brigades of the Party of God'

Kataeb Hezbollah, or Brigades of the Party of God, is an Iran-sponsored Shiite paramilitary group in Iraq. Although the group was officially founded in April 2007, its leaders have been actively engaged in anti-Western pro-Iran activities since the 1980s and expanded their influence beginning in 2003 following the U.S. invasion of Iraq.

The U.S. State Department describes Kataeb Hezbollah as "a radical Shia Islamist group with an anti-Western establishment and jihadist ideology." The U.S. State Department designated the group as a terrorist organization in July 2009.

FILE - Fighters from the Kataeb Hezbollah, or Hezbollah Brigades militia, inspect the destruction at their headquarters in the aftermath of a U.S. airstrike in Qaim, Iraq, Dec. 30, 2019.

On its official website, the group says it is an Islamic jihadist organization striving to, among other objectives, "foil the American project in the region, by defeating the occupation and expelling it from Iraq, failed and humiliated."

The Shiite group publicly supports the Guardianship of the Jurist, a system of governance in Shiite Islam that gives the Islamic jurist guardianship over people and by which the Iranian theocrats rule. As such, Kataeb Hezbollah's members see Iran's Supreme Leader Ayatollah Ali Khamenei as their own spiritual leader.

"The establishment of the Islamic Republic in Iran is only an essential stage in preparing the ground for the State of Divine Justice and an example of the rulings of Islam and the Guardianship of the Jurist," the group says on its website.

Structure

Kataeb Hezbollah is a part of Iraq's Popular Mobilization Forces (PMF), an umbrella organization of several Iraqi Shiite militias formed in 2014 to push back against the Sunni extremist group Islamic State (IS) following the collapse of the Iraqi army in 2014.

An August report by the U.S. Military Academy's Combating Terrorism Center said Kataeb Hezbollah had only about 400 active members in Iraq in 2011, while it now controls several PMF brigades with about 10,000 fighters. Of that number, some 2,500 fighters have been assigned to Syria while the rest are engaged in operations in Iraq, according to the report.

Little is known about the organization's leadership structure due to its secretive nature, but Jamal Jaafar Ibrahimi, more commonly known by his nom de guerre Abu Mahdi al-Muhandis, is at the top of its pyramid.

Abu Mahdi al-Muhandis, center, a commander in the Popular Mobilization Forces, attends a funeral procession of Hashd al-Shaabi (paramilitary forces) members, who were killed by U.S. airstrikes in Qaim district, in Baghdad, Iraq, Dec. 31, 2019.

Al-Muhandis, a U.S. designated terrorist, is accused by the U.S. and its Arab allies of participating in the bombing of Western embassies in Kuwait and the attempted assassination of the Emir of Kuwait in the early 1980s. He is technically the deputy commander of the PMF, but his strong influence within the group has made him its de facto leader.

Since the defeat of the Islamic State in Iraq in December 2017, Kataeb Hezbollah has increased its efforts to gain political representation by directly participating in Iraqi parliamentary elections. The Fatih Alliance, a political alliance of Shiite militias that entered the 2018 elections with Kataeb Hezbollah's participation, won  the second-highest number of votes for the Iraqi parliament.

Additionally, the group has expanded its outreach to Iraqi society by establishing groups that recruit Shiite intellectuals, women and youths, such as the Academic Elites Foundation and al-Zainabiyat Foundation.

Ties to Iran and foreign Shiite groups

Kataeb Hezbollah is seen by many Iraq observers as the central nervous system of Iran's Islamic Revolutionary Guards Corps Quds Force (IRGC-QF) in Iraq.

According to the U.S. government, Abu Mahdi al-Muhandis is an adviser to IRGC-QF commander Qassem Soleimani. It accuses the IRGC-QF of providing Kataeb Hezbollah with "lethal support" to target U.S.-led coalition and Iraqi security forces.

FILE - Revolutionary Guard General Qassem Soleimani, center, attends a meeting in Tehran, Iran, in this Sept. 18, 2016, photo released by an official website of the office of the Iranian supreme leader.

Financially, the group is believed by the U.S. to have received millions of dollars from Tehran to fund its various operations through Iraq and Syria. A lawsuit in November 2014 by U.S. veterans and family members of American soldiers killed in Iraq alleged that Iranian banks had funneled more than $100 million to militant groups such as Kataeb Hezbollah in Iraq.

The U.S. officials believe that Lebanon's Hezbollah militant group has also provided weapons and training for Kataeb Hezbollah members in Iran.

Future influence

Since defeating the Islamic State group, Iraqi officials have said one of their main priorities is to rebuild the country by putting paramilitary groups under the full control of the Iraqi Ministry of Defense.

Following several unclaimed attacks by suspected Shiite militias against Iraqi military bases hosting U.S. personnel, Iraqi Prime Minister Adel Abdul-Mahdi in July issued a decree asking all PMF groups, including Kataeb Hezbollah, to become an "indivisible part of the armed forces and be subject to the same regulations." He threatened that any group failing to comply by July 31 will be treated as an outlaw.

However, five months into the decree, militant groups such as Kataeb Hezbollah continue to operate outside of the Iraqi government control with no meaningful curtailment in their power, experts say.

Michael Knights, an Iraq military expert at the Washington Institute for Near East Policy, told VOA Persian that Tuesday's violent scenes at the gates of the U.S. embassy in Baghdad have embarrassed Iraqi government officials who face pressure from the U.S. to act against anti-American militias. But, he said, it is unlikely that the Iraqi government can restrain Kataeb Hezbollah anytime soon.

Dozens of angry Iraqi Shi'ite militia supporters damage property inside the U.S. embassy compound in Baghdad, Iraq, Dec 31, 2019.

"KH [Kataeb Hezbollah] can shoot dead policemen on the streets of Baghdad and refuse to surrender the murderers to Iraqi justice. KH can threaten ministers, can take over the Civil Aviation Authority of Iraq, and nobody will stand in their way. As a result, KH is very unlikely to face any negative action as a result of either the killing of a U.S. contractor or the blockading of the U.S. embassy in Baghdad," Knights told VOA.

Iraqi bases housing U.S. personnel have been attacked at least 10 times since October, with U.S. officials mostly blaming Iran-backed Iraqi Shiite militias.

An assault last Friday on a military base in Kirkuk province killed an American contractor and wounded several U.S. and Iraqi military personnel, prompting the U.S. to respond by striking five Kataeb Hezbollah facilities in Iraq and Syria on Sunday.

Clare Lopez, a former CIA career operations officer and an analyst at the Center for Security Policy, said that by responding to the attack in Kirkuk, the U.S. wanted to convey to Iran and its proxies that it is willing to respond should its interests be targeted in the region.

"The Iraqi people know that Washington has always supported Baghdad's government and provided with them the security and military aid they asked for," Lopez told VOA. "The U.S. strikes on Kataeb Hezbollah should not be construed as a violation of the Iraqi people's rights or an insult to them, but as a proper response to Iran's bullying via its proxies in Iraq."