Iran struck back at the United States for the killing of a top Iranian general early Wednesday, firing a series of ballistic missiles at two Iraqi bases housing US troops and warning the United States and its allies in the region not to retaliate.

The strikes by Iran were a major escalation of tensions that have been rising steadily across the Middle East following months of threats and attacks after US President Donald Trump's decision to unilaterally withdraw America from Tehran's nuclear deal with world powers.

Iranian state TV said the attack was revenge for the US killing of Revolutionary Guard General Qassem Soleimani, whose funeral procession Tuesday in his hometown of Kerman prompted angry calls to avenge his death.

Iran says it has launched "tens" of surface-to-surface missiles at Iraq's Ain Assad air base housing US troops over America's killing of a top Iranian general.

 

This tweet from Iranian state TV shows their footage.

The Pentagon is confirming that Iran has launched "more than a dozen ballistic missiles" at two targets hosting against US military and coalition forces in Iraq.

US Defense Department spokesman Jonathan Hoffman said "It is clear that these missiles were launched from Iran."

He says the attacks "targeted at least two Iraqi military bases" at Ain Assad and Irbil.

Hoffman says the US is "working on initial battle damage assessments."

Ain Assad air base is in Iraq's western Anbar province. It was first used by American forces after the 2003 US-led invasion that toppled dictator Saddam Hussein. It later saw American troops stationed there amid the fight against the Islamic State group in Iraq and Syria.

State TV said the operation's name was "Martyr Soleimani." It said the Guard's aerospace division that controls Iran's missile program launched the attack. Iran said it would release more information later.

The US also acknowledged another missile attack on a base in Irbil in Iraq's semiautonomous Kurdish region.

Iran's Revolutionary Guard warned the US and its regional allies against retaliating over the missile attack. The Guard issued the warning via a statement carried by Iran's state-run IRNA news agency.

"We are warning all American allies, who gave their bases to its terrorist army, that any territory that is the starting point of aggressive acts against Iran will be targeted," The Guard said. It also threatened Israel.

Soleimani's killing and Iran's missile strikes also marked the first time in recent years that Washington and Tehran have attacked each other directly rather than through proxies in the region.

It raised the chances of open conflict erupting between the two nations, which have been foes since the days immediately following Iran's 1979 Islamic Revolution.

After the strikes, a former Iranian nuclear negotiator posted a picture of the Islamic Republic's flag on Twitter, appearing to mimic Trump who posted an American flag following the killing of Soleimani and others Friday in a drone strike in Baghdad.

Wednesday's revenge attack came a mere few hours after crowds in Iran mourned Soleimani and as the US continued to reinforce its own positions in the region and warned of an unspecified threat to shipping from Iran in the region's waterways, crucial routes for global energy supplies.

US embassies and consulates from Asia to Africa and Europe issued security alerts for Americans. The US Air Force launched a drill with 52 fighter jets in Utah, just days after Trump threatened to hit 52 sites in Iran.

A stampede broke out Tuesday at Soleimani's funeral, and at least 56 people were killed and more than 200 were injured as thousands thronged the procession, Iranian news reports said.

As the crowds mourned Soleimani, more angry calls rose from Iran to avenge his death, drastically raising tensions in the Middle East.

Tuesday's deadly stampede took place in Soleimani's hometown of Kerman as his coffin was being borne through the city in southeastern Iran, said Pirhossein Koulivand, head of Iran's emergency medical services.

There was no information about what set off the crush in the packed streets, and online videos showed only its aftermath: people lying apparently lifeless, their faces covered by clothing, emergency crews performing CPR on the fallen, and onlookers wailing and crying out to God.

"Unfortunately as a result of the stampede, some of our compatriots have been injured and some have been killed during the funeral processions," Koulivand said, and state TV quoted him as saying that 56 had died and 213 had been injured.

Soleimani's burial was delayed, with no new time given, because of concerns about the huge crowd at the cemetery, the semi-official ISNA news agency said.

A procession in Tehran on Monday drew over 1 million people in the Iranian capital, crowding both main avenues and side streets in Tehran. Such mass crowds can prove dangerous. A smaller stampede at the 1989 funeral for Ayatollah Ruhollah Khomeini killed at least eight people and injured hundreds.

Hossein Salami, Soleimani's successor as leader of the Revolutionary Guard, addressed a crowd of supporters gathered at the coffin in a central square in Kernan. He vowed to avenge Soleimani, who was killed in a US drone strike Friday near Baghdad's airport.

"We tell our enemies that we will retaliate but if they take another action we will set ablaze the places that they like and are passionate about," Salami said.

"Death to Israel!" the crowd shouted in response, referring to one of Iran's longtime regional foes.

Salami praised Soleimani's work, describing him as essential to backing Palestinian groups, Yemen's Houthi rebels and Shiite militias in Iraq and Syria. As a martyr, Soleimani represented an even greater threat to Iran's enemies, Salami said.

Soleimani will ultimately be laid to rest between the graves of Enayatollah Talebizadeh and Mohammad Hossein Yousef Elahi, two former Guard comrades killed in Iran's 1980s war with Iraq. They died in Operation Dawn 8, in which Soleimani also took part. It was a 1986 amphibious assault that cut Iraq off from the Persian Gulf and led to the end of the war that killed 1 million.

The funeral processions in major cities over three days have been an unprecedented honour for Soleimani, seen by Iranians as a national hero for his work leading the Guard's expeditionary Quds Force.

The US blames him for killing US troops in Iraq and accused him of plotting new attacks just before he was killed. Soleimani also led forces supporting Syrian President Bashar Assad in that country's civil war, and he also served as the point man for Iranian proxies in countries like Iraq, Lebanon and Yemen. Russian President Vladimir Putin met with Assad in Syria on Tuesday amid the tensions between Washington and Tehran.

Soleimani's slaying already has led Tehran to abandon the remaining limits of its 2015 nuclear deal with world powers as his successor and others vow to take revenge.

In Iraq, pro-Iranian factions in parliament have pushed to oust American troops from Iraqi soil following Soleimani's killing. Germany and Canada announced plans to move some of their soldiers in Iraq to neighbouring countries.

According to a report on Tuesday by the semi-official Tasnim news agency, Iran has worked up 13 sets of plans to avenge Soleimani's death. The report quoted Ali Shamkhani, the secretary of Iran's Supreme National Security Council, as saying that even the weakest among them would be a "historic nightmare" for the US He declined to elaborate,

"If the US troops do not leave our region voluntarily and upright, we will do something to carry their bodies horizontally out," Shamkhani said.

The state-run IRNA news agency later published a statement from the Supreme National Security Council denying Shamkhani made the comment.

The US Maritime Administration warned ships across the Middle East, citing the rising threats. "The Iranian response to this action, if any, is unknown, but there remains the possibility of Iranian action against US maritime interests in the region," it said.

Oil tankers were targeted in mine attacks last year that the US blamed on Iran. Tehran denied responsibility, although it did seize oil tankers around the crucial Strait of Hormuz, the narrow mouth of the Persian Gulf through which 20 per cent of the world's crude oil travels.

The US Navy's Bahrain-based 5th Fleet said it would work with shippers in the region to minimise any possible threat.

The 5th Fleet "has and will continue to provide advice to merchant shipping as appropriate regarding recommended security precautions in light of the heightened tensions and threats in the region," 5th Fleet spokesman Commander Joshua Frey told The Associated Press.

Meanwhile, Iranian General Alireza Tabgsiri, the chief of the Guard's navy, issued his own warning.

"Our message to the enemies is to leave the region," Tabgsiri said, according to ISNA. The Guard routinely has tense encounters with the US Navy in the Persian Gulf.

Separately, Iran summoned the British ambassador over comments by Prime Minister Boris Johnson and the British defense minister about Soleimani's killing, the semi-official Mehr news agency reported.

Iran's parliament, meanwhile, has passed an urgent bill declaring the US military's command at the Pentagon and those acting on its behalf in Soleimani's killing as "terrorists," subject to Iranian sanctions. The measure appears to be in response to a decision by Trump in April to declare the Revolutionary Guard a "terrorist organisation."

The US Defense Department used that terror designation to support the strike that killed Soleimani. The action by Iran's parliament was done by a special procedure to speed it into law and also saw the lawmakers approve funding for the Quds Force with an additional 200 million euros, or about US$224 million.

Also Tuesday, Iranian Foreign Minister Mohammad Javad Zarif said the US had declined to issue him a visa to travel to New York for meetings at the United Nations. As the host of the UN headquarters, the US is supposed to allow foreign officials to attend such meetings.

"This is because they fear someone will go there and tell the truth to the American people," Zarif said. "But they are mistaken. The world is not limited to New York. You can speak with American people from Tehran too and we will do that."

Asked about Zarif, US Secretary of State Mike Pompeo told journalists America would comply with its obligations under UN rules to grant visas. He then referred to the Iranian diplomat as "a propagandist of the first order."

A US official who wasn't authorised to speak on the record said the application couldn't be processed in time for Zarif's travel although it wasn't clear if his request had been formally denied. A formal rejection would trigger legal technicalities that could affect future visa applications and could violate the host country agreement the US has with the UN.