Iran has threatened that they will retaliate after the death of Iran's elite Quds Force commander, Qasem Soleimani due to the US airstrike. Soleimani was the man behind the growing military force of the nation in the Middle East.
The 62-year-old deceased general was held as the second most powerful figure in Iran after Supreme Leader Ayatollah Ali Khamenei. Iraqi militia commander Abu Mahdi al-Muhandis, who was an adviser to Soleimani also fell prey to the attack.
The airstrike which took place during midnight was authorized by the US President Donald Trump. This has started an escalation in a shadow war in the Middle East between Iran and the US along with its allies.
The hostilities between Iran and US escalated after an attack which took place at the US embassy in Iraq by pro-Iranian militiamen who were following an air raid by the US on the Kataib Hezbollah paramilitary group, last week.
Responding to Friday's attack, Iraq's prime minister said Washington had violated a deal for keeping US troops in his country.
Israel put its army on high alert and US allies in Europe including Britain, France and Germany voiced concerns about an escalation in tensions.
The Pentagon said the "US military has taken decisive defensive action to protect US personnel abroad by killing Qasem Soleimani". Trump ordered the strike to disrupt future Iranian attack plans, it said.
US officials, speaking on condition of anonymity, said Soleimani was killed in a drone strike. Iran's Revolutionary Guards said he died in an attack by US helicopters.
The U.S. embassy in Baghdad urged all American citizens to depart Iraq immediately. US employees of foreign oil companies in Basra were preparing to leave the country, but Iraq's oil ministry said output and exports were unaffected.
Oil prices jumped more than $3 a barrel over concern about disruption to Middle East supplies.
Khamenei said harsh revenge awaited the "criminals" who killed Soleimani and said his death would double resistance against the United States and Israel.
In statements carried by state media, he called for three days of national mourning and appointed Soleimani's deputy, Brigadier General Esmail Ghaani, to replace him as Quds Force head.
US Secretary of State Mike Pompeo, speaking on Fox News, defended the strike as lawful, adding that the risk of doing nothing regarding Iran was enormous.
While the United States did not seek war with Iran it would not stand by and see American lives put at risk, he said.
'HEROES NEVER DIE'
As leader of the Quds Force, the foreign arm of the Revolutionary Guards, Soleimani had a key role in fighting in Syria and Iraq.
Over two decades he was at the forefront of projecting the Islamic Republic's military influence across the Middle East, acquiring celebrity status at home and abroad.
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.
President Hassan Rouhani said the assassination would make Iran more decisive in resisting the United States, while the Revolutionary Guards said anti-US forces would exact revenge across the Muslim world.
Hundreds of Iranians marched toward Khamenei's compound in central Tehran to convey their condolences.
"I am not a pro-regime person but I liked Soleimani. He was brave and he loved Iran, I am very sorry for our loss," said housewife Mina Khosrozadeh in Tehran.
In Soleimani's hometown, Kerman, people wearing black gathered in front of his father's house, crying as they listened to a recitation of verses from the Koran.
"Heroes never die. It cannot be true. Qasem Soleimani will always be alive," said Mohammad Reza Seraj, a high school teacher.
Democratic critics of Trump, a Republican, called the operation reckless.
"President Trump just tossed a stick of dynamite into a tinderbox," said former Vice President Joe Biden, a contender in this year's US presidential election.
Iraqi Prime Minister Adel Abdul Mahdi condemned the killings as an act of aggression that breached Iraq's sovereignty and would lead to war.
Israel has long regarded Soleimani as a major threat. Prime Minister Benjamin Netanyahu cut short a trip to Greece and Israeli Army Radio said the military was on heightened alert.
The slain commander's Quds Force, along with paramilitary proxies from Lebanon's Hezbollah to Iraq's Popular Mobilisation Forces grouping of Iran-backed militias - battle-hardened militias armed with missiles - has ample means to respond.
In September, US officials blamed Iran for a missile and drone attack on oil installations of Saudi state energy giant Saudi Aramco. Washington also blamed Tehran for earlier attacks on Gulf shipping.
Iran has denied responsibility for the strikes and accused Washington of warmongering by reimposing crippling sanctions on Iran's main export, oil, in order to force Tehran to renegotiate a deal to freeze its nuclear activities.
Soleimani had survived several assassination attempts against him by Western, Israeli and Arab agencies over the past two decades.
The Quds Force, tasked with carrying out operations beyond Iran's borders, shored up support for Syria's President Bashar al-Assad when he looked close to defeat in the civil war raging since 2011 and also helped militias defeat Islamic State in Iraq.
Soleimani became head of the force in 1998, after which he quietly strengthened Iran's ties with Hezbollah in Lebanon, Syria's government and Shi'ite militia groups in Iraq.
(With inputs from Reuters)