Sir Keir Starmer made clear that the UK “played no role” in the air strikes against Iran while still decrying the regime as “abhorrent”.
Speaking on Saturday, the prime minister talked of the threat the Islamic Republic posed to the Jewish community in Britain.
His comments came hours after the coordinated campaign by the US and Israel had got under way.
The Islamic Republic had responded with missiles launches against targets across the Gulf region in what Sir Keir called “indiscriminate strikes”.
Sir Keir said: “While the situation is evolving very quickly, I want to set out our response.
“The United Kingdom played no role in these strikes.
“But we have long been clear – the regime in Iran is utterly abhorrent.
“They have murdered thousands of their own people, brutally crushed dissent, and sought to destabilise the region.
“Even in the United Kingdom, the Iranian regime poses a direct threat to dissidents and the Jewish community.
“Over the last year alone, they have backed more than 20 potentially lethal attacks on UK soil.
“So it’s clear – they must never be allowed to develop a nuclear weapon.
“That remains the primary aim of the United Kingdom and our allies – including the US.”
While the UK has not taken part in the air strikes, its forces continued to be deployed in the region, the prime minister said: “British planes are in the sky today as part of coordinated regional defensive operations to protect our people, our interests, and our allies.”
Sir Keir called upon Iran to “end this now”, urging the regime to “refrain from further strikes, give up their weapons programmes, and cease the appalling violence and repression against the Iranian people”.
He suggested such “de-escalation” would be a route “back to the negotiating table”, even while further exchanges continued between Iran and the US and Israel.
A joint statement by the UK, France and Germany as the E3 made clear none of the three states had taken part in the military.
It read: “France, Germany and the United Kingdom have consistently urged the Iranian regime to end Iran’s nuclear program, curb its ballistic missile program, refrain from its destabilising activity in the region and our homelands, and to cease the appalling violence and repression against its own people.
“We did not participate in these strikes, but are in close contact with our international partners, including the United States, Israel, and partners in the region. We reiterate our commitment to regional stability and to the protection of civilian life.
“We condemn Iranian attacks on countries in the region in the strongest terms. Iran must refrain from indiscriminate military strikes. We call for a resumption of negotiations and urge the Iranian leadership to seek a negotiated solution. Ultimately, the Iranian people must be allowed to determine their future.”
President of the EU commission Ursula von der Leyen said on Saturday afternoon a special “security college” would be convened on Monday to address the situation.
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