US and Israeli strikes against Iran are not “legal in a way that the UK would recognise”, a former UK national security adviser has warned.

Explosions were heard over Tehran on Saturday morning after the coordinated “preventative attack”, which has prompted retaliatory strikes from Iran towards Israel.

President Donald Trump confirmed a “major combat operation” in an eight-minute speech posted to Truth Social, stating Iran could never have a nuclear weapon and adding: “It’s been mass terror, and we’re not going to take it any longer.”

Sir Keir Starmer is set to chair an emergency COBRA security meeting on Saturday morning and has increased military and security at the UK’s military bases in Cyprus. The UK did not participate in the strikes.

The UK government is at odds with the Trump administration, having denied permission for the US to use RAF bases for the strikes because of concerns over international law.

That sentiment was echoed by Peter Ricketts, the UK’s former national security advisor, who said the UK would not consider the attacks legal.

He told BBC Radio 4’s Today programme: “None of this, I think, is in any sense legal in a way that the UK would recognise.

“There was really no imminent threat to the US. This is action that they chose to undertake, or were dragged into it by the Israelis.”

Lord Ricketts added that the Israeli government had “pre-empted any risk that the US-Iranian negotiations were going to reach some sort of deal on the nuclear programme”.

Responding to news of the strikes, a UK government spokesperson said: “Iran must never be allowed to develop a nuclear weapon and that is why we have continually supported efforts to reach a negotiated solution.

“Our immediate priority is the safety of UK nationals in the region and we will provide them with consular assistance, available 24/7.

“As part of our longstanding commitments to the security of our allies in the Middle East, we have a range of defensive capabilities in the region, which we have recently bolstered. We stand ready to protect our interests. We do not want to see further escalation into a wider regional conflict.”

The UK and US have been at odds over Middle East policy, with Sir Keir refusing to take a role in Trump’s Board of Peace for Gaza, although former prime minister Sir Tony Blair has accepted a seat on it.

President Trump was also angered over the UK’s decision, along with France and other allies, to recognise the state of Palestine.

But the row over the use of RAF bases in Cyprus to bomb Iran is also understood to have had wider implications, with President Trump withdrawing his support for Sir Keir’s Chagos Islands deal to cede the British territory to Mauritius.

Meanwhile, a senior Labour MP has warned that the UK should resist being drawn into a conflict in the Middle East.

Dame Emily Thornberry, chairwoman of the Commons Foreign Affairs Committee, told BBC Radio 4’s Today programme she did not think the US-Israeli strikes were legal.

She said: “As far as I’m aware, we’re not involved in this. There’s not been British agreement to be involved in this, and I think that’s the right thing to do. I don’t think that there’s a legal basis for this action.”

She added: “They were not under imminent threat, and so it’s therefore difficult to see what the legal justification is.”

Asked whether the UK should resist being drawn into the conflict, Dame Emily said: “Absolutely, unless we’re attacked ourselves, which, as I say, unfortunately this morning, we don’t know whether we will be because there may be attacks by the Iranians on Western bases in the Arab Gulf, and so then the situation may change.

“We just don’t know.”