The United States killing of Iranian General Qassem Soleimani has changed the rules of engagement between Iran and the US, Iranian analysts say.

Soleimani, who for 20 years was the face of Iranian militarised foreign policy in the Middle East, was killed in a US air raid in Iraq at Baghdad's international airport in the early morning hours of Friday.

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He was the head of Iran's elite Islamic Revolutionary Guard Corps (IRGC) Quds Force and the architect of its military and political power.

Soleimani died alongside Abu Mahdi al-Muhandis, the deputy commander of Hashd al-Shaabi (Popular Mobilisation Forces, PMF), an umbrella of Iraqi militias. While the PMF has been legally integrated into Iraq's formal security forces, critics say some of the factions still operate independently of Baghdad and that some are funded and armed through the IRGC.

The White House and the Pentagon confirmed the killing of Soleimani in Iraq, saying the attack was carried out at the direction of US President Donald Trump and was aimed at deterring future attacks allegedly being planned by Iran.

Iran's supreme leader Ayatollah Ali Khamenei said in a statement carried by Iranian state television that "harsh revenge" awaited the "criminals" who killed Soleimani.

Iranian political analyst Mohammad Marandi told Al Jazeera that the US would regret the killings, which he described as an "act of war" against Iran and Iraq.

Marandi said the US has "changed the rules of engagement with Iran in killing such a high profile Iranian military and government official". He said the killing has practically "united Iran and Iraq's hands to attack the US soldiers and other westerners in Iraq".

Soleimani was a revered military figure in Iran because of his role in unifying Iraqi and Iranian-backed militias that rolled back the Islamic State if Iraq and the Levant (ISIL or ISIS) group gains in Iraq in 2015. He "was instrumental in their ultimate defeat", Foad Izadi of Tehran University told Al Jazeera.

Marandi said Soleimani was beloved in Iran, in stark contrast with the perception that was constructed of him by Western media, which often portrayed him as a "shadowy figure".

"He was not shadowy at all. He was very well known to the public and was often seen giving public speeches on national occasions," Marandi said.

Iranian analyst Abas Aslani told Al Jazeera that Soleimani was an influential personality in Iranian society and played a major role in Iran's foreign policy.

He said the killing will usher a "new chapter" in Iran's political and military behaviour in the Middle East.

"This killing will not deter Iran from keeping up with its foreign policy strategies in the region," he added.

'Mistake'

Former CIA intelligence officer Bob Baer said the killing of Soleimani was a major "mistake" on the part of the US, adding that Tehran's reaction could escalate US-Iran tensions very quickly.

"The CIA has no real intelligence operations inside Iran and no one in the Trump administration understands the Iranian mentality", Baer said.

He added that the killing has put US troops and US citizens in Iraq and in the region at great risk, especially since the US has no combat troops in Iraq and the Iraqi army is too weak to defend the US embassy or other US interests in Iraq.

"Because of this, no one can predict how the blowback to this operation will unfold," Baer told Al Jazeera.

Gulf impact

Marandi, the analyst, said the US's Gulf allies, such as Saudi Arabia and the United Arab Emirates (UAE), may end up "paying for the US action because they have been part of the US alliance to attack Iran".

Although the UAE has strong commercial and economic ties with Iran, it has for years, along with Saudi Arabia, lobbied the US to confront Iran's assertive geopolitical policies in the Gulf and in the region.

Both the UAE and Saudi Arabia have been fighting a war in Yemen against Houthi rebels.

Saudi Arabia has no diplomatic ties with Iran and has often urged US policymakers to respond to Iran's regional military involvements more aggressively.

Follow Ali Younes on Twitter: @ali_reports