Hundreds of drones and missiles are surging towards Israel after Iran launched a retaliatory attack.
Iran's Islamic Revolutionary Guards Corps confirmed on Saturday evening that it had launched the strikes in response to what it called an Israeli strike on its Damascus consulate on April 1.
The attack at the start of the month killed seven Guards officers including two senior commanders.
Israel's military said sirens would sound in any threatened areas and that its defences were poised to deal with them.
It is expected that the missiles will take a number of hours before they arrive.
Rishi Sunak condemned “in the strongest terms” Iran’s “reckless attack” against Israel.
An anti-missile system operates after Iran launched drones and missiles towards Israel, as seen from Ashkelon, Israel
REUTERS
Objects are seen in the sky above Jerusalem after Iran launched drones and missiles towards Israel
REUTERS
The Prime Minister said the UK will “continue to stand up for Israel’s security and that of all our regional partners, including Jordan and Iraq” following the regional escalation.
In a statement on Saturday night, Sunak said: “I condemn in the strongest terms the Iranian regime’s reckless attack against Israel.
“These strikes risk inflaming tensions and destabilising the region.
“Iran has once again demonstrated that it is intent on sowing chaos in its own backyard.
“The UK will continue to stand up for Israel’s security and that of all our regional partners, including Jordan and Iraq.
“Alongside our allies, we are urgently working to stabilise the situation and prevent further escalation. No-one wants to see more bloodshed.”
US President Joe Biden has cut short his trip to Delaware to return to the White House for urgent talks with his national security team.
White House National Security Council spokesperson Adrienne Watson said in a statement: "President Biden has been clear: our support for Israel’s security is ironclad.
Benjamin Netanyahu has called bis war cabinet for meetings
REUTERS
Iranians took to the streets to celebrate after the strikes were ordered
GETTY
Iranians celebrated the retaliatory strikes from their government against Israel
GETTY
"The United States will stand with the people of Israel and support their defence against these threats from Iran."
RAF Typhoons from Akrotiri, Cyprus, have been deployed to help protect Israel.
British and American warplanes have already downed some Israel-bound Iranian drones over the Iraq-Syria border area.
The Ministry of Defence said in a statement: "In response to increased Iranian threats and the growing risk of escalation in the Middle East, the UK Government has been working with partners across the region to encourage de-escalation and prevent further attacks.
"We have moved several additional Royal Air Force jets and air refuelling tankers to the region. These will bolster Operation Shader, which is the UK’s existing counter-Daesh operation in Iraq and Syria. In addition, these UK jets will intercept any airborne attacks within range of our existing missions, as required.
"We will continue to cooperate closely with our regional partners in the interest of de-escalation."
Israel had been anticipating some sort of retaliatory action from Iran for a number of days.
Earlier this week the Islamic Republic vowed to get revenge on for the April 1 air strike.
Four days ago Iran's Supreme Leader said Israel 'must be punished'
REUTERS
Joe Biden returned to the White House earlier than planned in order to hold security meetings on the unfolding situation
REUTERS
"When they attacked our consulate area, it was like they attacked our territory," Ayatollah Ali Khamenei said in a televised speech on Wednesday.
"The evil regime must be punished, and it will be punished."
The Gaza war between Israel and Hamas, now in its seventh month, has driven up tensions in the region, spreading to fronts with Lebanon and Syria and drawing long-range fire at Israeli targets from as far away as Yemen and Iraq.
Those clashes now threaten to morph into a direct open conflict pitting Iran and its regional allies against Israel and its main supporter the United States.
With the entire Middle East on alert, Jordan, Lebanon and Iraq have all shut their air space.
Syria, an ally of Iran, said it was putting its ground-to-air defence systems around the capital and major bases on high alert, army sources there said.
Egypt, one of the biggest regional powers, urged "utmost restraint".