Trump warns Iran of 'major retaliation' in case of attack

US President Donald Trump has warned Iran of "major retaliation" if Tehran carries out any attack against America to avenge the killing of top military commander Qasem Soleimani and hinted at striking its cultural sites.

His statement came hours after Iran announced it will no longer abide by the limits contained in the 2015 landmark nuclear deal.

Maj Gen Soleimani, 62, the head of Iran's elite al-Quds force and architect of its regional security apparatus, was killed when a US drone fired missiles into a convoy that was leaving the Baghdad International Airport early on Friday. The strike also killed the deputy chief of Iraq's powerful Hashed al-Shaabi paramilitary force.

Soleimani's killing was the most dramatic escalation yet in spiralling tensions between Iran and the US.

Trump, on his way to the White House from Mar-a-Lago resort in Florida after spending his Christmas and New Year vacation, told reporters abroad Air Force One: "If it happens it happens. If they do anything there will be major retaliation".

"They're allowed to kill our people. They're allowed to torture and maim our people. They're allowed to use roadside bombs and blow up our people. And we're not allowed to touch their cultural site? It doesn't work that way," Trump said in response to a question.

Meanwhile, Trump spoke to British Prime Minister Boris Johnson.

"The two leaders discussed the current situation in Iraq and Iran and reaffirmed the close alliance between the two countries," the White House said.

On Saturday night, Trump warned that the US will target 52 sites in Iran some of which are "at a very high level and important to Iran and the Iranian culture" if the Islamic republic attacks American personnel or assets.

Responding to Trump's remarks, Iranian Foreign Minister Javad Zarif said targeting cultural sites was a 'war crime'.

Supreme Leader of Iran Ayatollah Khamenei has vowed a revenge against the killing of his general, saying "severe revenge awaits the criminals" behind the attack.

Soleimani was widely seen as the second most powerful figure in Iran behind the Supreme Leader Ayatollah Ali Khamenei. His Quds Force, an elite unit of the Iranian Revolutionary Guards, reported directly to the Ayatollah Khamenei and he was hailed as a heroic national figure.