Rishi Sunak has called on “all sides” to “show restraint” after Iran’s attack on Israel on Saturday.
The PM said he would speak to his Israeli counterpart Benjamin Netanyahu to express solidarity and also discuss how to prevent “further escalation”.
Mr Sunak told MPs Iran’s actions had been “reckless and dangerous”.
Tehran launched more than 300 drones and missiles at Israel in retaliation for a deadly air strike on its consulate in Damascus.
Israel said 99% of the projectiles had been intercepted with help from allies – including the US, UK and Jordan.
In a statement in the House of Commons, Mr Sunak confirmed the RAF had intercepted “a number of Iranian drones” and said the air force was “the best of the best”.
He said Iran had “once again shown its true colours” and its attack had been intent on “further destabilising the Middle East”.
“Saturday’s attack was the act not of the people but of a despotic regime, and it is emblematic of the dangers that we face today,” Mr Sunak said, adding that threats to stability were “growing, not just in the Middle East but everywhere”.
He said the UK was “working urgently with our allies to de-escalate the situation and prevent further bloodshed”.
“We want to see calmer heads prevail and we’re directing all our diplomatic efforts to that end,” Mr Sunak said.
Turning to the ongoing war between Israel and Hamas, he said “nothing that has happened over the last 48 hours affects our position on Gaza”.
Mr Sunak said it was “Israel’s right, and indeed it’s duty, to defeat the threat from Hamas” but also reiterated his calls for a “long-term and sustainable ceasefire”.
Labour leader Sir Keir Starmer said he “welcomed the prime minister’s call for restraint” and that the attack “left the world a more dangerous place”.
He added: “If diplomacy takes centre stage, and it must, then we also need to be clear diplomatic premises should not be targeted and attacked. That is a point of principle.”
The strike on Iran’s consulate in Syria on 1 April killed seven Islamic Revolutionary Guard Corps officers officers, including a top commander.
The Iranian government has accused Israel of carrying out that attack, but Israel has neither confirmed nor denied it.
Earlier, Foreign Secretary Lord Cameron told the BBC the UK had joined Israel’s defence against Iran in order to prevent an escalation of the conflict.
He said the attack – which he described as a “double defeat” for Iran because it had been “almost wholly unsuccessful” and also showed they were a “malign influence in the region” – could have resulted in thousands of casualties and led to greater escalation had it been successful.
Lord Cameron urged Israel to be “smart” and “tough” as it considers its response.
Speaking to BBC Radio 4’s Today programme, the former prime minister added that Israel should turn its focus once more to the situation in Gaza and securing a deal to get the hostages home.
Lord Cameron added that the UK did not support a retaliatory strike, echoing US President Joe Biden’s comment that Israel should “take the win”.
The UN Secretary General Antonio Guterres and Germany’s foreign minister Annalena Baerbock have also called for calm, while French President Emmanuel Macron said France would do everything possible to avoid what he described as a regional conflagration.
Israel’s cabinet and opposition leaders have met in Tel Aviv to consider their response to the attack.
Herzi Halevi, chief of staff of the Israel Defense Forces (IDF), said Iran’s attacks would be “met with a response” and said Israel was considering its next steps.
Earlier, a spokesperson for the UK prime minister said the country and its allies were “clearly not briefed” by Tehran, in response to Iran’s assertion that it gave advanced warning of the attack.
Attack drones were intercepted by the RAF in Syrian and Iraqi airspace, where it was already operating with the US as part of the Operation Shader mission against the Islamic State group.
Lord Cameron confirmed the UK’s role was to “backfill” for the US and the RAF had agreed to shoot down Iranian drones if they came through that airspace.
The Ministry of Defence has not said how many RAF Typhoons were airborne, nor how many weapons it shot down.
The war in Gaza was triggered after waves of Hamas gunmen stormed into Israel, killing about 1,200 people and taking more than 250 hostage.
Israel vowed to eliminate Hamas and has launched retaliatory operations in Gaza which have killed more than 33,000 people, including thousands of children, according to the Hamas-run health ministry.
Israeli Prime Minister Mr Netanyahu had been coming under increasing international pressure over how his government was handling the conflict, including over allowing more access to aid.
Source: BBC