Six Britons are dead and another 10 are missing after the assault by Hamas on southern Israel a week ago, Rishi Sunak has said. Speaking in the Commons for the first time since the outbreak of war a week ago, the prime minister told MPs that some of those missing were feared dead, though it was proving difficult to identify all of those who had been killed in the attack. “With a heavy heart I can inform the house that at least six British citizens were killed,” Sunak said. “A further 10 are missing, some of whom are thought to be among the dead. We are working with Israel to establish the effects as quickly as possible. And we are supporting the families who are suffering unimaginable pain.” The missing include two teenage sisters, Noiya, 16, and Yahel, 13, the Guardian has been told. It is unclear if they were included in the 10 to which the prime minister referred. Their relatives have not yet released the teenagers’ surname. It is understood that their mother, Lianne, was killed in the attack. Sunak also announced the UK would spend an extra £10m on humanitarian aid to Gaza, where 2,750 people have been killed in Israeli airstrikes and hundreds of thousands are now living without access to electricity and limited access to water. Britain has bolstered its military presence in the Mediterranean, while the prime minister has embarked on a flurry of diplomacy as part of an international effort to prevent the war becoming a broader regional conflict. Finally, the prime minister said the government would provide an extra £3m to the Community Security Trust, a charity that helps to protect British Jews, after a rise in reports of antisemitic attacks in the UK. Sunak said: “We should call [the Hamas attack] by its name: it was a pogrom.” But he also urged Israel to act according to international humanitarian law in its response and avoid civilian casualties where possible. In a shift in tone from some of his comments last week, Sunak said: “We will continue to call on Israel to take every possible precaution to avoid harming civilians. I repeat President Biden’s words: as democracies we are stronger and more secure when we act according to the rule of law.” Keir Starmer, the Labour leader, struck a similar note. “Labour stands with Israel; Britain stands with Israel,” he said “Israel has the right to bring her people home, to defend herself, to keep its people safe.” But he added: “Israel’s defence must be conducted in accordance with international law. Civilians must not be targeted, innocent lives must be protected. There must be humanitarian corridors. There must be humanitarian access, including food, water, electricity and medicines.” Starmer is facing a growing revolt from some of his own grassroots members, however, who complain that he has not done enough to condemn Israeli actions in cutting off water and electricity to Gaza. In the last few days, four Labour councillors, one former MP and an officer of Young Labour have all said they would resign from the party in protest against Starmer’s unwillingness to condemn Israeli tactics in Gaza. Every MP who spoke on the matter in the Commons on Monday condemned the Hamas assault, in which attackers killed 1,300 people and captured 199 more. But responses were broadly split between those who expressed unalloyed support for Israel and occasionally urged action against Iran, and those who wanted the prime minister to take stronger action to prevent a humanitarian disaster in Gaza. Liam Fox, the Conservative who is one of parliament’s staunchest pro-Israeli MPs, said: “If the fingers on the trigger were Hamas, the strings being pulled were from Tehran … Isn’t it time that we in this country asked again why Iranian banks are operating from the City of London, why Iran Air is operating from Heathrow airport, and why again we have not proscribed the IRGC [the Islamic Revolutionary Guard Corps, Iran’s powerful militia group], as I believe we should have?” To some groans from the Tory benches, the leftwing Labour MP Richard Burgon said: “The horrific acts by Hamas do not justify responding with collective punishment of the Palestinian people … Such collective punishment is a war crime under the Geneva convention.” Burgon was not the only MP to warn about the danger of Israel handing out collective punishment to Palestinians in Gaza. Alicia Kearns, the Conservative chair of the foreign affairs select committee, said: “We can support Israel and grieve with their people whilst recognising that how a counter-terrorism operation is conducted matters.” She added: “The people of Gaza are not Hamas [and] 1.2 million children bear no collective guilt for Hamas’s terror.” In one of the most personal and emotionally resonant contributions, the Liberal Democrat MP Layla Moran told fellow MPs her extended family were Palestinian Christians who had been caught up in the fighting in Gaza. “Their house was bombed by the IDF [Israel Defence Forces],” she said. “They went to seek sanctuary in a church because we’re Christian Palestinians. I’m afraid to say they’re still there because they’re too old to go and because they say to me they have nowhere to go.” She urged the prime minister to ensure there would be a Palestinian state at the end of the conflict. Sunak replied: “We must find a way to bring about peace and stability in the region.”