The flare-up of violence in the Middle East, ignited by a wide-ranging Hamas attack on Israel at the weekend, has already claimed at least 2,400 lives.
Downing Street said maritime patrol and surveillance planes will begin flying in the region from Friday to track threats, including monitoring activity such as the “transfer of weapons to terrorist groups”.
A Royal Navy task group will be moved to the eastern Mediterranean next week as a contingency measure to back humanitarian efforts, it added.
Alongside our allies, the deployment of our world-class military will support efforts to ensure regional stability and prevent further escalation
The military package includes P8 aircraft, surveillance assets, two Royal Navy ships – Royal Fleet Auxiliary (RFA) vessels Lyme Bay and Argus – three Merlin helicopters and a company of Royal Marines.
The British armed forces will be on stand-by to “deliver practical support to Israel and partners in the region, and offer deterrence and assurance”, No 10 said.
The deployment appears to represent a shift in approach to Britain’s military involvement, with the Prime Minister’s official spokesman earlier this week saying there were “no plans to redeploy UK military assets to Israel”.
Mr Sunak said: “We must be unequivocal in making sure the types of horrific scenes we have seen this week will not be repeated.
“Alongside our allies, the deployment of our world-class military will support efforts to ensure regional stability and prevent further escalation.
“Our military and diplomatic teams across the region will also support international partners to re-establish security and ensure humanitarian aid reaches the thousands of innocent victims of this barbaric attack from Hamas terrorists.”
The Prime Minister has also asked for all British military teams in Israel, Cyprus and across the region to be bolstered.
Defence Secretary Grant Shapps said: “The Royal Navy Task Group, RAF operations and our wider military support will be an undeniable display of the UK’s resolve to ensure Hamas’s terrorist campaign fails, whilst reminding those who seek to inflame tensions that the forces of freedom stand with the Israeli people.”
John Healey, Labour’s shadow defence secretary, said his party “backs these military moves” as part of the UK’s response to Hamas’s incursion that left hundreds of Israelis dead.
“We stand in solidarity with Israel at this dark hour,” he tweeted.
The military deployment comes ahead of Mr Sunak’s trip to Sweden for the Joint Expeditionary Force summit where he is due to speak with northern European leaders about the situations in Israel and Ukraine.
The Prime Minister’s attention has also been focused on the conflict’s impact on British communities, having announced an additional £3 million to provide extra security for the UK’s Jewish population.
The money will be given to the Community Security Trust (CST) after the group, which acts on the behalf of British Jews on matters of policing and racism, said it had recorded a 400% spike in antisemitic incidents in the UK since the weekend’s assault.
No 10 said the additional funding will enable the CST to place additional guards at schools it supports and allow for additional security staff outside synagogues on Friday nights and Saturday mornings when Jews are marking the sabbath.
The King held a private audience with the Chief Rabbi at Buckingham Palace to personally express his concern for the Jewish community in the UK, the palace said.
Following the meeting, Sir Ephraim Mirvis said the King’s words offered strength “at this dark time”.
Sir Ephraim also met with Labour Party leader Sir Keir Starmer on Thursday.
Sir Keir, in a statement released afterwards, said the rise in antisemitic incidents was “appalling” and that harassment or intimidation towards Jewish communities was “utterly unacceptable”.
With the conflict between Israel and Gaza worsening, the UK Government has organised flights to help British nationals leave Israel.
The first flight was expected to leave the Israeli city of Tel Aviv on Thursday, the Foreign Office said, with further flights planned in the coming days subject to the security situation.
The UK has also sent a rapid deployment team to assist British citizens on the ground.
International aid groups have warned that deaths in Gaza could accelerate as Israel prevents the passage of food, water, fuel and medicine into the territory and after the region’s only power station ran out of fuel.
The International Committee of the Red Cross said hospitals in Gaza risk turning into morgues when their generators run out.
The United Nations World Food Programme (WFP) warned that crucial supplies were running dangerously low in the Gaza Strip.
“It’s a dire situation in the Gaza Strip that we’re seeing evolve with food and water being in limited supply and quickly running out,” said Brian Lander, the deputy head of emergencies at WFP.
There have been calls for corridors to be established to allow aid in and civilians out as Israel continues to fire retaliatory strikes on the 25-mile strip, which is ruled by Hamas.
Israeli Prime Minister Benjamin Netanyahu has vowed that “every Hamas member is a dead man”, with reports suggesting a ground offensive into Gaza is being prepared — a move likely to increase the death toll.
Sadiq Khan, the Labour mayor of London, has written to Foreign Secretary James Cleverly pushing for “urgent action” to deliver humanitarian access to Gaza following similar calls by the United Nations and the World Health Organisation.
Labour’s shadow foreign secretary David Lammy also urged “for food, water, medicines and electricity” supplies to be made available.
Alicia Kearns, Conservative chairwoman of the Foreign Affairs Select Committee, told LBC that Tel Aviv has “a duty under international humanitarian law” to ensure those in Gaza have access to medical aid and water.
“We can get the humanitarian aid in but no-one else can switch back on water apart from the Israelis,” she said.
The Foreign Office published a video on social media on Thursday of Mr Cleverly speaking during his visit to Israel.
The Cabinet minister said the UK supported Israel’s “right to defend itself” and “right to recover the people who have been kidnapped”.
He made no mention of the situation in Gaza during the 30-second clip.