Sir Keir Starmer marked "a day of sorrow and grief" one year on from the 7 October attacks on Israel, as he called for the "immediate and unconditional" release of hostages still being held in Gaza.
Speaking in the Commons, the prime minister praised the "dignity and determination" of the families of those taken captive by Hamas.
He said of them: "Their pain is as acute today as it was a year ago. They live it every day."
Hamas gunmen killed around 1,200 people and took 250 hostages when the group launched a surprise assault on communities in southern Israel. A British-Israeli woman is among 97 hostages still unaccounted for.
Sir Keir described the 7 October attacks as being "born of hatred" and "targeted not just at individuals, but at Jewish communities, at their way of life and at the state of Israel, the symbol of Jewish security to the world".
He paid tribute to 15 British citizens killed in the initial raids, and another who has since died in captivity. A total of 97 hostages remain unaccounted for.
Among them is Mandy Damari, a 28-year-old British-Israeli woman.
Earlier on Monday, her mother Mandy described the "living hell" of not knowing her daughter's fate, and called on the British government to do more to secure the release of hostages.
She told an event in London: “How is it that she is still imprisoned there after one year?
"Why isn't the whole world, especially Britain, fighting every moment to secure her release? She's one of their own."
Foreign Secretary David Lammy attended the same event. He said: "It is a day of deep reflection and pain thinking about 7 October, the worst attack on the Jewish community since the Holocaust."
The 7 October attacks led to the Israeli government launching an invasion into Gaza in an attempt to free the hostages and dismantle Hamas.
In the months that followed, hate crime against Jews and Muslims in the UK rose amid protests and enflamed community tensions.
During his Commons statement on Monday, Sir Keir said his government would "stand with all communities here in the UK, against hatred of Jews and Muslims".
The prime minister reflected on victims in the conflict which has broken out in the Middle East in the aftermath of the attack.
Israeli assaults on Gaza have killed nearly 42,000 Palestinians and war has spread to Israel's northern border with Lebanon.
The Lebanese armed group Hezbollah - which, like Hamas, is proscribed as a terrorist organisation in the UK, US and European Union - began almost daily rocket attacks against Israel in support of Hamas shortly after the 7 October attacks.
Hundreds of people have died in Lebanon in recent days in Israeli bombardments.
The prime minister said: "Nobody in this House can truly imagine what it feels like to cower under the bodies of your friends, hoping a terrorist won't find you minutes after dancing at a music festival.
"No one can truly imagine seeing your city, your homes, your hospital, your businesses obliterated, with your neighbours and family buried underneath.
"It is beyond our comprehension - and with that should come humility."
Sir Keir said the government would continue to push for a ceasefire agreement in Gaza and a long-term diplomatic solution which provides security to Israel, alongside side a Palestinian state.
