Hundreds of thousands of people flooded streets in Iran on Sunday to walk alongside a casket carrying the remains of a top Iranian general killed in a U.S. airstrike in Baghdad, a slaying which has caused Iran to abandon limits of an unravelling nuclear deal with world powers.

Gen. Qassem Soleimani's body was flown from Iraq to the southwestern Iranian city of Ahvaz and an honour guard stood as mourners carried the flag-draped coffins of Soleimani and other Revolutionary Guard members off the tarmac.

The caskets then moved slowly through streets choked with mourners wearing black, beating their chests and carrying posters with Soleimani's portrait. Demonstrators also carried red Shia flags, which traditionally symbolize the spilled blood of someone unjustly killed and call for their deaths to be avenged.

Ahvaz is a city that was a focus of fighting during the bloody, 1980-88 war between Iraq and Iran in which the general slowly grew to prominence. After that war, Soleimani joined the Guard's newly formed Quds, an elite force that works with Iranian proxy forces in countries like Iraq, Lebanon and Yemen.

Nuclear deal limits abandoned

Following the procession, Iran said Sunday it would no longer abide by any of the limits of its 2015 nuclear deal, abandoning the accord's key provisions that block Tehran from having enough material to build an atomic weapon.

Iran insisted in a state television broadcast it remained open to negotiations with European partners, who so far have been unable to offer Tehran a way to sell its crude oil abroad despite U.S. sanctions. It also didn't back off of earlier promises that it wouldn't seek a nuclear weapon.

Iranians march behind a vehicle carrying the coffins of slain Maj.-Gen. Soleimani and others as they pay homage in Mashhad. Iran decided to cancel a similar procession in Tehran due to the overwhelming turnout by mourners in Mashhad, the Revolutionary Guards said. (Mohammad Taghi/Tasnim News/AFP via Getty Images)

However, the announcement Sunday represents the clearest nuclear proliferation threat yet made by Iran since Trump unilaterally withdrew from the accord in May 2018. It also further raises regional tensions, as Iran's longtime foe Israel has promised never to allow Iran to be able to produce an atomic bomb.

Iran's state TV cited a statement by President Hassan Rouhani's administration saying the country will not observe limitations on its enrichment of uranium, the amount of stockpiled enriched uranium as well as research and development into nuclear activities.

"The government of the Islamic Republic of Iran has in a statement announced its fifth and final step in reducing Iran's commitments under the JCPOA," a state TV broadcaster said, using an acronym for the deal. "The Islamic Republic of Iran no longer faces any limitations in operations."

It did not elaborate what levels it would immediately breach in its nuclear program.

French President Emmanuel Macron, who in September offered a $15 billion US bailout to Iran in an effort to save the failing nuclear deal, expressed solidarity with its allies during a telephone conversation with Trump on Sunday and said Iran must avoid "destabilizing" actions.

"Given the recent rise in tensions in Iraq and the region, the President of the Republic highlighted his total solidarity with our allies in light of the attacks carried out in recent weeks against the coalition in Iraq," Macron's office said in a statement.

"He also expressed his concerns regarding the destabilizing activities of the Quds force under General Qassem Soleimani and highlighted the need for Iran... to avoid taking any measures that could lead to an escalation in the situation and destablizing the region."

U.K. Prime Minister Boris Johnson also said Sunday that he had spoken with Macron, Trump and German Chancellor Angela Merkel about Iran, saying he was "in close contact with all sides to encourage de-escalation."

"Given the leading role [Soleimani] has played in actions that have led to the deaths of thousands of innocent civilians and Western personnel, we will not lament his death," Johnson said in a statement.

However, Johnson said it was clear that calls for retaliation or reprisals would "simply lead to more violence in the region" which was in "no one's interest."

U.S. military 'will pay the price'

Retaliation for Soleimani's death could potentially come through the Quds' proxy forces. His longtime deputy Esmail Ghaani already has taken over as as the unit's commander.

The leader of one such proxy, Lebanon's Hezbollah, said Soleimani's killing made U.S. military bases, warships and service members spread across the region fair targets for attacks. In a speech Sunday, Nassan Nasrallah said evicting U.S. military forces from the region is now a priority and that the U.S. military "will pay the price."

A former leader of Iran's Revolutionary Guard on Sunday said the Israeli cities of Tel Aviv and Haifa could be targeted to avenge the drone strike. Mohsen Rezaee made the comment in Tehran at a ceremony in honour of the slain general.

He has previously alleged Israel somehow leaked information about Soleimani's whereabouts to U.S. forces, who killed him early last Friday morning, striking his convoy as it left Baghdad's airport.

People attend a funeral procession in Ahvaz, Iran, for Soleimani and Iraqi militia commander Abu Mahdi al-Muhandis, who were killed in a U.S. drone strike at Baghdad airport. (Hossein Mersadi/Fars news agency/West Asia News Agency via Reuters)

After the procession through Ahvaz, authorities took Soleimani's body to Mashhad, but then cancelled a Tehran ceremony to honour the slain general due to an overwhelming turnout by mourners in the second city, Mashhad, the Revolutionary Guards said. His remains will go to Qom on Monday, followed by a burial in his hometown of Kerman on Tuesday.

This marks the first time Iran has honoured a single man with a multi-city ceremony. Not even the Islamic Republic's founder, Ayatollah Ruhollah Khomeini received such a processional with his death in 1989. Soleimani on Monday will lie in state at Tehran's famed Musalla mosque as the revolutionary leader did before him.

Soleimani was the architect of Iran's regional policy of mobilizing militias across Iraq, Syria and Lebanon, including in the war against the Islamic State group. He was also blamed for attacks on U.S. troops and American allies going back decades.

Iraq moves to expel U.S. troops

Iraq's parliament, meanwhile, voted on Sunday in favour of a resolution calling for an end to the foreign military presence in their nation, an effort aimed at expelling the 5,000 U.S. troops stationed there during the war against Islamic State in Iraq and Syria (ISIS).

An Iranian holds a poster of slain Iraqi paramilitary chief al-Muhandis, left, and Iranian Maj.-Gen. Soleimani during a ceremony in the northwestern city of Ahvaz to honour the men, both killed in a U.S. drone strike. (Hossein Mersadi/Iran's Farsi News Agency/AFP via Getty Images)

The Iranian parliament opened with legislators chanting: "Death to America!" Parliamentary speaker Ali Larijani compared Soleimani's killing to the 1953 CIA-backed coup that cemented the shah's power and to the U.S. Navy's downing of an Iranian passenger plane in 1988 that killed 290 people. He also described American officials as following "the law of the jungle."

While parliamentary resolutions are non-binding to the Iraqi government, this one is likely to be heeded: Prime Minister Adel Abdul Mahdihad earlier called on parliament to end foreign troop presence as soon as possible.

There was no immediate comment on the Iraqi move from the U.S. State Department or Pentagon.

Iran-backed Iraqi militia commander Qais al-Khazali said if U.S. troops do not leave Iraq, they would be considered an occupying force.

The U.S. sanctioned Khazali's Asaib Ahl al-Haq group on Friday, saying it was an Iranian proxy.

Soleimani's killing escalated the crisis between Tehran and Washington after months of trading attacks and threats. The conflict is rooted in Trump pulling out of Iran's atomic accord and imposing sanctions that have crippled Iran's economy. Iran has promised "harsh revenge" for the U.S. attack on a man many saw as a pillar of the Islamic Republic.

Although it's unclear how or when Iran may respond, any retaliation was likely to come after three days of mourning declared in both Iran and Iraq.

U.S. hit on other targets would be 'a war crime'

Late Saturday, Trump wrote on Twitter afterward that the U.S. had already "targeted 52 Iranian sites (representing the 52 American hostages taken by Iran many years ago), some at a very high level & important to Iran & the Iranian culture."

Iranian Foreign Minister Mohammad Javad Zarif said any U.S. targeting of Iranian cultural sites would be a war crime. (Kirill Kudryavtsev/AFP via Getty Images)

Trump did not identify the targets but added that they would be "HIT VERY FAST AND VERY HARD."

He followed this threat on Sunday by saying that the U.S. "will quickly and fully strike back, and perhaps in a disproportionate manner" if Iran were to attack any American person or target.

These Media Posts will serve as notification to the United States Congress that should Iran strike any U.S. person or target, the United States will quickly & fully strike back, & perhaps in a disproportionate manner. Such legal notice is not required, but is given nevertheless! —@realDonaldTrump

Iranian senior ministers responded Sunday to Trump's threat, saying the attacks would be a "war crime" and comparing the U.S. president to Hitler and Genghis Khan.

Iranian Foreign Minister Mohammad Javad Zarif tweeted that the Trump administration had already "committed grave breaches of [international] law" and that "targeting cultural sites is a war crime."

-Having committed grave breaches of int'l law in Friday's cowardly assassinations, <a href="https://twitter.com/realDonaldTrump?ref_src=twsrc%5Etfw">@realdonaldtrump</a> threatens to commit again new breaches of JUS COGENS;<br><br>-Targeting cultural sites is a WAR CRIME;<br><br>-Whether kicking or screaming, end of US malign presence in West Asia has begun. —@JZarif

The 1954 Hague Convention, of which the U.S. is a party, bars any military from "direct hostilities against cultural property." However, such sites can be targeted if they have been re-purposed and turned into a legitimate "military objective," according to the International Committee of the Red Cross.

Iran, home to 24 UNESCO World Heritage sites, has in the past reportedly guarded the sprawling tomb complex of Ayatollah Ruhollah Khomeini with surface-to-air missiles.

U.S. Secretary of State Mike Pompeo said that any target the U.S. military may strike in Iran, in the event Iran retaliates, would be legal under the laws of armed conflict.

The U.S. Embassy in Saudi Arabia has separately warned Americans "of the heightened risk of missile and drone attacks."