UK forces were involved in supporting Israel in the conflict in the Middle East after Iran launched a missile attack on the country.
Defence Secretary John Healey said British forces had “this evening played their part in attempts to prevent further escalation”, without giving more details.
The BBC understands UK fighter jets were involved, as they were in April when Iran last attacked Israel with missiles.
Responding on Tuesday to Iran’s attack, during which the Israeli military said about 180 missiles were fired with most intercepted, Prime Minister Sir Keir Starmer said the UK “stands with Israel” and recognises its right to self-defence.
Iran’s Islamic Revolutionary Guard Corps said it had launched the missiles in retaliation for recent attacks that killed the leaders of the Hezbollah and Hamas militant groups, as well as a senior Iranian commander.
Healey said: “British forces have this evening played their part in attempts to prevent further escalation in the Middle East.
“I want to thank all British personnel involved in the operation for their courage and professionalism.
“The UK stands fully behind Israel’s right to defend its country and its people against threats.”
In April British jets shot down a number of drones fired at Israel from Iran.
The drones were intercepted by the RAF in Syrian and Iraqi airspace, where it was already operating as part of the Operation Shader mission against the Islamic State group.
The decision to use jets in April was taken by the previous Conservative government and supported at the time and since by Sir Keir.
Sir Keir used the address from Downing Street to condemn Iran’s attack on Israel, saying he was “deeply concerned that the region is on the brink”.
“We stand with Israel and we recognise her right to self-defence in the face of this aggression,” he said.
Calling on Iran to stop its attacks, he added: “Together with its proxies like Hezbollah, Iran has menaced the Middle East for far too long, chaos and destruction brought not just to Israel, but to the people they live amongst in Lebanon and beyond.
“Make no mistake, Britain stands full square against such violence. We support Israel’s reasonable demand for the security of its people.”
Sir Keir was on the phone to his Israeli counterpart Benjamin Netanyahu when the Iranian attacks began.
The two men had been speaking for around 15 minutes – about the prospect of missiles being fired by Tehran – when Netanyahu had to abandon the call because he had been told the attacks were under way.
During their call, Sir Keir also underlined the importance of a ceasefire in Lebanon and Gaza.
Conservative Party leader Rishi Sunak said: “We stand unequivocally by Israel’s right to defend itself including against Hezbollah in Lebanon.”
In his statement, the prime minister repeated his advice to British nationals to leave Lebanon, warning the situation was becoming “increasingly grave”.
He added: “If you have the means to leave, the time is now. Do not wait.”
Britons in Lebanon have been advised to register their presence with officials on the government’s website and a UK-chartered plane is leaving Beirut on Wednesday.
But some told the BBC they had received no confirmation or details about their booking on the government-chartered flight, despite paying for a seat.
As of last week, there were thought to be between 4,000 and 6,000 UK nationals, including dependants, in Lebanon.
The missile attack came hours after Israel launched a ground invasion in southern Lebanon, in what it has described as “limited, localised and targeted” raids against Hezbollah.
Lebanese officials say more than 1,000 people have been killed following Israeli air strikes over the past two weeks. Hezbollah has responded by firing hundreds of rockets into northern Israel.
The previously sporadic cross-border fighting between Israel and Hezbollah escalated on 8 October 2023 – the day after the unprecedented attack on Israel by Hamas gunmen from the Gaza Strip – when Hezbollah fired at Israeli positions, in solidarity with the Palestinians.