He promised to make a statement to the nation on Wednesday morning about the increasingly precarious situation with Iran.

Mr Trump offered no immediate indication of whether he would retaliate, and stayed out of sight as news of the missile strikes emerged.

But he tweeted that an assessment of casualties and damages was under way. The initial outlook, he said, was "So far, so good!"

Iran struck back at the US for the killing of a top Iranian general, firing a series of ballistic missiles at two Iraqi bases housing US troops in Iraq.

Nicola Sturgeon: UK must not get dragged into Iran conflict

Revenge attack

Rockets were filmed being allegedly launched from Iran against the US military base in Ein-al Asad in Iraq.

Iranian state TV said it was in revenge for the US killing of Revolutionary Guard General Qassem Soleimani, whose death last week in an American drone strike near Baghdad prompted calls for avenge.

General Soleimani's killing and the strikes by Iran came as tensions have been rising steadily across the Middle East after President Donald Trump's decision to unilaterally withdraw America from Tehran's nuclear deal with world powers.

They 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 enemies, which have been at odds since Iran's 1979 Islamic Revolution.

Iran initially announced only one strike, but US officials confirmed both.

Protesters demonstrate over the U.S. airstrike in Iraq that killed Iranian Revolutionary Guard General Qassem Soleimani in Tehran, Iran. Picture: Getty

A warning to American allies

US defence officials were at the White House, probably to discuss options with Mr Trump, who launched the strike on Soleimani while facing an upcoming impeachment trial in the Senate,

Iran's Revolutionary Guard warned the US and its regional allies against retaliating over the missile attack against the Ain al-Asad air base in Iraq's western Anbar province. 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," it said. It also threatened Israel.

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

Ain al-Asad

Ain al-Asad air base was first used by American forces after the 2003 US-led invasion that toppled dictator Saddam Hussein, and later saw American troops stationed there amid the fight against the Islamic State group in Iraq and Syria. It houses about 1,500 US and coalition forces.

Two Iraqi security officials said at least one of the missiles appeared to have struck a plane at the base, igniting a fire. It was not immediately clear whether it was an Iraqi or US jet.

About 70 Norwegian troops also were on the airbase but no injuries were reported, Brynjar Stordal, a spokesperson for the Norwegian Armed Forces told the Associated Press.

Mr Trump visited the sprawling Ain al-Asad airbase, about 100 miles west of Baghdad, in December 2018, making his first presidential visit to troops in the region.

He did not meet with any Iraqi officials at the time, and his visit inflamed sensitivities about the continued presence of US forces in Iraq. Vice President Mike Pence also has visited the base.

Martyr Soleimani

Iranian state TV said the Guard's aerospace division that controls Iran's missile program launched the attack, which it said was part of an operation called Martyr Soleimani.

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

"As we evaluate the situation and our response, we will take all necessary measures to protect and defend US personnel, partners and allies in the region," said Jonathan Hoffman, an assistant to the US defence secretary.

Wednesday's revenge attack happened just hours after crowds in Iran mourned Gen Soleimani at his funeral. It also came 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.

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

The stampede took place in Gen Soleimani's hometown of Kerman as his coffin was being borne through the city in south-eastern Iran, said Pirhossein Koulivand, head of Iran's emergency medical services.

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

General 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.

Iran launches missile attack on US bases in Iraq