Trump threatens to hit Iran with 'never before seen force' if it retaliates against strikes that killed supreme leader

Donald Trump has threatened further action against Iran if the country responds to a wave of US and Israeli strikes in which Supreme Leader Ayatollah Ali Khamenei was killed.

Khamenei was the leader of Iran since 1989, taking over after the death of Ruhollah Khomeini who had secured the Shia Islamist faction's ascendancy after the 1979 revolution.

Over the weekend, the US and Israel carried out a series of strikes against Iran.

At the time of the strikes the US had been negotiating with the Islamic Republic about its nuclear program, with Trump previously threatening action if they didn't reach an agreement.

Following the US and Israeli attacks, which hit multiple cities across Iran including Tehran, the country responded with missile and drone attacks across the region.

Early on Sunday, Iranian officials confirmed that Khamenei had been killed in the strikes, and the Iranian government has now vowed to avenge him.

Khamenei has been killed in the strikes (Iranian Leader Press Office/Anadolu via Getty Images)

Iranian parliamentary speaker Mohammad Bagher Qalibaf gave a televised address on Sunday, calling the US 'filthy criminals'.

He said: “You have crossed our red line and must pay the price.

"We will deliver such devastating blows that you yourselves will be driven to beg.”

But Trump has now threatened more action against Iran if it retaliates further.

Taking to his social media platform Truth Social, Trump wrote: “Iran just stated that they are going to hit very hard today, harder than they have ever hit before."

He then went on to threaten further action if Iran were to retaliate, writing: "THEY BETTER NOT DO THAT, HOWEVER, BECAUSE IF THEY DO, WE WILL HIT THEM WITH A FORCE THAT HAS NEVER BEEN SEEN BEFORE! Thank you for your attention to this matter!"

Strikes have hit cities across Iran including in Tehran (Majid Saeedi/Getty Images)

Iran has been ruled by the Islamic Republic since the revolution of 1979.

The current hardline Islamist government was able to seize power after a popular uprising against the Shah, Mohammad Reza Pahlavi.

Pahlavi was a pro-western dictator installed after democratically-elected socialist Mohammad Mosaddegh was overthrown in a coup orchestrated by the UK and US after he nationalised British oil interests in the country.

Since seizing power the Islamic Republic has pursued hardline conservative policies including forcing women to cover their hair, and having severe punishment for things like drinking alcohol, as well as responding violently to protests against the regime.

The government has also actively sought to expand its influence in the Middle East, including through its Revolutionary Guard Corps and Quds Force.

This has also included proxy groups including Hezbollah in Lebanon and also Syria, and Kataib Hezbollah in Iraq.