The US strike on Baghdad international airport targeted a convoy carrying Soleimani and the deputy head of Iraq's powerful Hashed al-Shaabi force, Abu Mahdi al-Muhandis.

The raid has confirmed the worst fears of many Iraqis -- that their homeland will become the main battlefield in a looming conflict between Iran and the United States.

Slamming the strike as an "aggression," Iraq's caretaker prime minister Adel Abdel Mahdi said it would "spark a devastating war in Iraq."

Fanar Haddad of Singapore University's Middle East Institute said: "Iran's strongest cards are in Iraq, and I think that Iraq will pay the price for this."

Tensions between the United States and Iran have been rising for months, as Washington accused Tehran-backed factions of firing rockets on their troops across Iraq and on their embassy in Baghdad.

But they have soared over the past week.

On December 27, a rocket attack killed a US contractor working in northern Iraq, prompting retaliatory US strikes that killed 25 fighters from Kataeb Hezbollah, a hardline Hashed faction.

Angry Hashed supporters laid siege to the US embassy as Washington announced hundreds of new US troops were en route to the region.

- Path to war? -

But Washington delivered its most decisive blow yet early Friday when a volley of strikes hit near Baghdad international airport, leaving two cars torched on the access highway.

Iran's Revolutionary Guards confirmed Soleimani was killed in the strike, while the Hashed announced Muhandis's death.

With the two dead, the Quds Force -- the Guards' foreign operations arm -- has been left decapitated and the Hashed lost its de facto chief, too.

Iran's supreme leader Ayatollah Ali Khamenei vowed "severe revenge" for the raid and its top security body was meeting to discuss options.

Analysts said the outbreak of a wider conflict was looking increasingly likely.

"If Iran does need to respond and make a performance out of this, the fear is that there will be something more than just loading rockets at embassies," said Haddad.

"It could set Iraq along the path of internal conflict and that's something Iran can very easily instigate," he said.

The nature of the strike is unpredecented because of the seniority of those targeted -- making its repercussions hard to picture, said Ramzy Mardini, a researcher at the US Institute of Peace.

"The problem with judging what happens next is a problem of imagination. Nobody thought this was in the realm of possibility," he told AFP.

"It's likely that all actors on all sides will be playing things by ear in the short term, which is a recipe for miscalculation," said Mardini.

- 'Heads will roll' -

Friday's strike had shown that Iran could no longer use its allies in Iraq to carry out attacks against US interests "without risking an American conventional retaliation on Iran," Mardini told AFP.

"Plausible deniability has gone out the window."

The US had expressed increasing frustration with the escalating rocket attacks on its 5,200 troops in Iraq and on its embassy in Baghdad.

US forces led the 2003 invasion against then-dictator Saddam Hussein and Washington has worked closely with Iraqi officials and commanders since then.

But its influence has waned compared with that of Iran, which carefully crafted personal ties with Iraqi politicians and armed factions, even during Saddam's reign.

Soleimani was the prime example, sweeping into Baghdad regularly to hold meeting with top Iraqi officials during times of turmoil.

Ranj Alaaldin, a fellow at the Brookings Institution in Doha, said that would leave Iran with a range of questions for its Iraqi partners.

"How did the US know of Soleimani's arrival in Baghdad? Who leaked the intel?" Alaaldin tweeted.

"Watch the Iraqi political space. Heads will roll."