Israel should show “restraint” as it prepares to invade Gaza, Britain’s foreign secretary has said, marking a change of tone from the UK government. James Cleverly urged the Israel Defence Forces to show “discipline” and avoid mass casualties, as it prepared to launch a ground attack a week after Hamas militants killed hundreds of Israeli civilians in terrorist attacks. He also confirmed that about 10 Britons were among those whom Hamas fighters had taken hostage during the attack. Cleverly told Sky News: “Restraint, discipline – these are the hallmarks of the Israeli Defence Force that I want to see. And indeed, those are the hallmarks of a high-functioning military organisation, which the IDF is, in stark contrast to the terrorist atrocities perpetrated by Hamas. “I’ve said, maintain that clear distinction: Israel seeks to avoid civilian casualties; Hamas seeks civilians in order to target.” Separately, he told the BBC the UK government had been lobbying Egypt to open the Rafah border crossing between Gaza and Egypt to allow people in Gaza to escape. They include British citizens, the foreign secretary confirmed on Sunday, adding that it would not be “an unreasonable estimate” to suggest that 10 Britons had been taken hostage by Hamas. However, he said he had not asked Israel to wait to launch its offensive until civilians had left northern Gaza, saying that Hamas was urging civilians to stay in place to use them as human shields. Cleverly’s comments contrasted with the unqualified support for Israel that other British ministers have offered in the days since Hamas’s assault, which killed more than 1,300 Israelis. Rishi Sunak, the prime minister, issued a 300-word statement on Saturday in which he pledged “unequivocal” support for Israel, “not just today, not just tomorrow, but always”. He added: “Britain is with you. What took place was an act of pure evil and Israel has every right to defend itself. We will do everything we can to support Israel in restoring the security it deserves.” Cleverly was speaking as Israeli tanks and personnel carriers moved into position for the expected ground assault. The Israeli military said it was preparing an “integrated and coordinated attack from the air, sea and land”. Israel gave people in northern Gaza 24 hours to evacuate their homes, something international agencies warned was impossible and which the UN said constituted “a blatant violation of international humanitarian law”. The World Health Organization has said that moving people out of hospitals in Gaza would be “tantamount to a death sentence”. Neither Cleverly nor David Lammy, Labour’s shadow foreign secretary, would say on Sunday whether they believed the evacuation order was illegal, however. Cleverly said: “I’m not a lawyer, but the UK’s position on international law is absolutely unwavering.” In a separate interview, Lammy said: “We have rules and those rules mean that you must minimise death … It’s hugely important that we minimise the loss of human life.” Labour believes the Conservatives are trying to paint them as being pro-Hamas. David Evans, the Labour general secretary, sent an email to his party’s MPs and councillors urging them not to attend pro-Palestinian protests this weekend, something party members have complained about. Lammy defended that advice on Sunday, saying: “It’s important that as we face and want to be the next government, that people do not share platforms with people who do not share Labour values, that they’re careful and cautious.”