The2003 invasion of Iraq led by the U.S., which toppled Iraqi presidentSaddam Hussein and hisArab Socialist Ba'ath Party, was the decisive event that allowedIran to begin exerting an unprecedented level of influence onIraqi politics.[1] Leveraging the fact thatShia Muslims account for the majority of the population in both countries, the Iranian government used Shia militias to serve Iran's interests during theIraq War.[2] This culminated in Iran's involvement in theIraqi insurgency, in which there were instances of Shia militants engaging theMulti-National Force in direct combat.[3][4] Organizations that enjoyed large-scale Iranian support included theMahdi Army ofMuqtada al-Sadr, as well asKata'ib Hezbollah,Asa'ib Ahl al-Haq, and thePromised Day Brigade. Since 2007, theUnited States has employed a"kill or capture" strategy with regard to confronting Iranian operatives in theIraqi conflict.
After condemning the September 11 attacks,[5][6] and expressing sympathy with bereaved Americans,[7] Iran briefly cooperated with the United States in late 2001, providing limited military support against the Taliban in Afghanistan, including operations in Herat.[8][9][10] However, in early 2002,president George W. Bush labeled Iran part of an "axis of evil" along with Iraq and North Korea,[11] sharply worsening relations. Iranian leaders across the political spectrum condemned the remark, viewing it as a strategic error that strengthened hardliners who favored a more confrontational stance toward the United States.[12][10]
In September 1980,Iraq under Saddam Hussein launched aninvasion of Iran in an unsuccessful attempt to annexoil-rich Iranian territory,[13][14]: 261 marking the beginning of awar that would last until 1988.[15] The Iran–Iraq War is regarded as being a major trigger for rising sectarianism in the region, as it was viewed by many as a clash between Sunni Muslims (Ba'athist Iraq and other Arab States)[16][17][18] and the Shia revolutionaries that hadtaken power in Iran.[19]
In a declassified 1991 report, theCIA estimated that Iran had suffered more than 50,000 casualties from Iraq's use of severalchemical weapons,[20] though modern estimates have reached more than 100,000, as the long-term effects continued to cause casualties;[21][22] they also show that the United States was providing reconnaissance intelligence to Iraq around 1987–88, which was then used to launch chemical weapon attacks on Iranian troops, and that the CIA fully knew that chemical weapons would be deployed andsarin andcyclosarin attacks followed.[23] According to Iraqi documents, assistance in developing chemical weapons was obtained from firms in many countries, including the United States.[24]
In January 2002, one year before the U.S.-led invasion of Iraq, bilateral relations between Iran and Iraq improved significantly when an Iranian delegation, led by Amir Hussein Zamani, visited Iraq for final negotiations to resolve the conflict through talks on issues ofprisoners of war and those who wentmissing in action during the Iran–Iraq War.[25]
In the aftermath of the2003 invasion of Iraq, Iran supported Shi'ite insurgent groups dubbed theSpecial Groups in Iraq, which were made up by theMahdi army,Kata'ib Hezbollah,Asa'ib Ahl al-Haq, and thePromised Day Brigade. The U.S. used the Iraqi government to fight these insurgents as a result.[26][27][28][29] A 2008 report by theCombating Terrorism Center atWest Point based on reports from the interrogations of dozens of captured Shia fighters described an Iranian-run network smuggling Shia fighters into Iran where they received training and weapons before returning to Iraq.[30][31]
According to two unnamed US officials,the Pentagon is examining the possibility that theKarbala provincial headquarters raid was supported by Iranians. In a speech on31 January 2007, Iraqi Prime MinisterNouri al-Maliki stated that Iran was supporting attacks against Coalition forces in Iraq,[32] and some Iraqis suspect that the raid may have been perpetrated by the Quds Force in retaliation for the detention of five Iranian officials by US forces in the northern Iraqi city ofIrbil on11 January.[33][34]
In 2007, tensions increased greatly betweenIran andIraqi Kurdistan due to the latter's giving sanctuary to the militant Kurdish secessionist groupParty for a Free Life in Kurdistan (PEJAK). According to reports, Iran had been shelling PEJAK positions in Iraqi Kurdistan since 16 August. These tensions further increased with an alleged border incursion on 23 August by Iranian troops who attacked several Kurdish villages killing an unknown number of civilians and militants.[35]
An estimated 150 Iranian intelligence officers, plus members of Iran'sIslamic Revolutionary Guard Corps, are believed to be active inside Iraq at any given time. For more than a year, U.S. troops have detained and recorded fingerprints, photographs, and DNA samples from dozens of suspected Iranian agents in a catch and release program designed to intimidate the Iranian leadership.[36]
Coalition forces alsobegan to target alleged Iranian Quds Force operatives in Iraq, eitherarresting or killing suspected members. The Bush administration and coalition leaders began to publicly state that Iran was supplying weapons, particularlyEFP devices, to Iraqi insurgents and militias although to date have failed to provide any proof for these allegations. Further sanctions on Iranian organizations were also announced by the Bush administration in the autumn of 2007. On 21 November 2007, Lieutenant General James Dubik, who is in charge of training Iraqi security forces, praised Iran for its "contribution to the reduction of violence" in Iraq by upholding its pledge to stop the flow of weapons, explosives, and training of extremists in Iraq.[37]
Hezbollah as Iran's proxy, formedUnit 3800 and sent elite Hezbollah operatives to Iraq to train local fighters. The unit's primary mission was to train and equip Iraqi Shiite militias, such as theMahdi Army,Asaib Ahl al-Haq, andKataib Hezbollah, enhancing their capabilities in guerrilla warfare, kidnappings, and the use of sophisticated improvised explosive devices (IEDs). Some Iraqi militants also received advanced training inLebanon. The unit then oversaw operations executed against U.S. andcoalition forces and provided funds, weapons, and logistical assistance to groups like theBadr Organization,Saraya al-Khorasani, and the al-Mahdi Army.[38][39]
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