Iran has issued a chilling two-word warning to Britain about its involvement in the crisis engulfing the Middle East, urging it to be “very careful”. The UK has so far stayed out of directly intervening in the war, which exploded when the US and Israel launched bombing raids on Tehran and killed its Supreme Leader, Ayatollah Ali Khamenei.

Britain has agreed to allow its airbases to be used by American forces for defensive operations, while RAF Typhoon and F-35 jets have been deployed to Qatar and Cyprus to defend allies from attack. But in an interview on Sunday With Laura Kuenssberg, Seyed Ali Mousavi, the Iranian ambassador to London, warned that his country would have a “right to self-defence” should the UK directly join US-Israeli operations. He added that Iran expected the British Government “to be very delicate, very careful”.

Sir Keir Starmer has come under intense pressure for Britain to support the US, with Donald Trump delivering a blistering attack on the British Prime Minister for his lack of help.

The US president said it was “not Winston Churchill we’re dealing with” in response to questions about Sir Keir.

Mr Mousavi welcomed Britain’s decision not to enter the conflict so far and said Iran’s response “depends on the activities of the Americans and the Israeli regime”.

He added that “there is no doubt we will defend ourselves” if attacks continue.

Iran has insisted it will not give up in its war with the US despite Mr Trump’s insistence that an unconditional surrender is the only way American and Israeli strikes will end.

Iranian president Masoud Pezeshkian issued a statement on the nation’s state TV IRNA channel in which he apologised to other Middle Eastern countries for strikes that had hit them, but insisted there would be no unconditional surrender.

Mr Pezeshkian said in a pre-recorded speech broadcast on Saturday: “The enemies must take their wish for the surrender of the Iranian people to their graves.”

Washington also warned of a forthcoming bombing campaign, which officials said would be the most intense so far.

The Trump administration has already approved a new $151million (£112.7million) arms sale to Israel after Mr Trump said he would not negotiate with the Islamic Republic.

Meanwhile, on Saturday evening, Dubai Marina was rocked by an explosion as Iran launched missiles and drones at the United Arab Emirates.