Iranian Foreign Minister Mohammad Javad Zarif has condemned the killing of General Qassem Soleimani, the head of Iran's elite Islamic Revolutionary Guard Corps' (IRGC's) Quds Force, in a US air strike at Baghdad International Airport as an "act of international terrorism".

"The US bears responsibility for all consequences of its rogue adventurism," Zarif said in a statement on Friday, warning that the move would strengthen resistance against the United States and Israel in the region and the world, Iranian state television reported.

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Iran often refers to regional countries and forces opposed to Israel and the US as a "resistance" front.

Soleimani, considered the architect of Iran's regional security apparatus, was killed along with at least six others following US air raids at Baghdad International Airport. Iraqi armed group commander Abu Mahdi al-Muhandis, an adviser to Soleimani and deputy commander of Iran-backed militias known as the Popular Mobilisation Forces (PMF) or Hashd al-Shaabi, was also killed in the attack.

Following the announcement, Iranian state television presenters wore black and broadcast footage of Soleimani peering through binoculars across a desert and greeting a soldier, and of Muhandis speaking to followers.

The high-profile killings come amid a sharp escalation in Iran-US tensions. On Tuesday, Iran-backed armed groups in Iraq and their supporters held a violent protest at the US embassy in Baghdad, setting fires and attempting to storm the heavily fortified compound.

The protest came after the US attacked sites in Iraq and Syria belonging to Kataib Hezbollah, an Iran-backed Iraqi militia founded by Muhandis and which falls under the Hashd al-Shaabi (PMF). At least 25 Kataib Hezbollah fighters were killed in the attack.

'Harsh retaliation'

Iran's Supreme Leader Ayatollah Ali Khamenei warned that "a harsh retaliation is waiting" and announced a three-day mourning in the country.

He said the killing of Soleimani, who he considered a close friend and confidant, would double the motivation of the resistance against the US and Israel.

"All enemies should know that the jihad of resistance will continue with a doubled motivation, and a definite victory awaits the fighters in the holy war," Khamenei said in a statement carried by state television.

Mohsen Rezaei, the former commander of Revolutionary Guard, also warned the US of "revenge".

"He [Soleimani] joined his martyred brothers, but we will take vigorous revenge on America," Rezaei, who is now the secretary of a powerful state body, said in a post on Twitter.

Reporting from Tehran, Al Jazeera's Dorsa Jabbari said a strong Iranian response was expected.

"There's a clear indication that there will be a military response at some point.

"It is seen as a hostile act on an Iranian general who was not there in an official military capacity. Qassem Soleimani was in Iraq on an advisory role.

"The supreme leader has said that this glorious, grandiose, and great fighter has now been martyred. He said he was one of the great followers of the late Ayatollah [Ruhollah] Khomeini, the founder of the Revolutionary Guard.

"His killing by the US is being seen as an act of war and it will certainly have a very strong response," Jabbari said.

Ordered killing

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.

The Pentagon said Trump had ordered Soleimani's "killing" after pro-Iran protesters this week stormed the US embassy in Baghdad.



Following Soleimani's death, Trump tweeted an image of the US flag without any further explanation.

A senior House Democrat said the US legislators were not told in advance of the attack ordered by Trump.

The strike conducted in Iraq against Soleimani "went forward with no notification or consultation with Congress", House Foreign Affairs Committee Chairman Eliot Engel said in a statement.

Soleimani was "the mastermind of immense violence" who has "the blood of Americans on his hands", the Democratic legislator said.

But "to push ahead with an action of this gravity without involving Congress raises serious legal problems and is an affront to Congress's powers as a coequal branch of government", Engel added.