His mother-in-law in besieged Gaza is running out of drinking water. His brother-in-law, a doctor, is dealing with the horror of trying to identify body parts in a hospital nearby. And his four-year-old daughter, at home in Scotland, can only understand that “granny is afraid of the thunder”. Humza Yousaf, Scotland’s first minister, has described in brutal detail the impact on trapped family members of Israel’s bombardment of Gaza in response to the shock attacks by Hamas at the weekend. In an interview, Yousaf renewed his calls for the UK foreign secretary, James Cleverly, to urge Israel “to agree to a ceasefire, open up a humanitarian corridor, let supplies come in but, importantly, let people come out”. He said: “The world can’t sit back and witness the obliteration of 2.2 million people. We are all going to have a stain on our conscience if we allow that to happen.” His wife’s parents, Elizabeth and Maged El-Nakla, who live in Dundee, travelled to Gaza last week to visit their son and four grandchildren and Maged’s 92-year-old mother, who is unwell. The couple have been unable to find safe passage out of Gaza since the first Hamas attack took place on the border with Israel on Saturday. On Wednesday, Yousaf’s wife, Nadia El-Nakla, told the BBC that her parents “continually tell me they feel like they’re going to die”. Speaking to the Guardian in Bute House, his official residence in Edinburgh, on Thursday, Yousaf said Nadia had earlier received another message from her mother. “It was another rough night, as you’d expect, and there was a lot of bombing in their neighbourhood,” he said. “The real worry for them is not just the airstrikes but the fact that they’re running really low on supplies. My mother-in-law said this morning they only have a few plastic bottles of clean drinking water left.” Yousaf’s brother-in-law is a doctor and, he said, one of the “overwhelming majority of people in Gaza [who] have nothing to do with Hamas, and many of them live in fear of Hamas”. Nadia last spoke to her brother on Wednesday evening. “He’s working constant shifts, manages to get home for a few hours kip and then he’s straight back out the door,” Yousaf said. “The things he has seen, no person should see. He’s been given the job of identifying the bodies for people. He says, ‘I’m trying to match body parts up, people that are decapitated, trying to match whose head goes with whose body’.” His parents-in-law’s household includes four children, one of whom is only two months old, cousins to Yousaf’s two daughters. “It feels like almost a hopeless situation and, frankly, I feel utterly helpless,” he said. “Both my kids are really close to their granny but my 14-year-old is really upset,” he added. He took her out for KFC and Starbucks on Wednesday afternoon in an unsuccessful attempt to distract her. He and his wife are struggling to explain to four-year-old Amal why her mother is upset. “She’s dead sweet … she’ll come up with a wee tissue and rub Nadia’s back. We’ve told her ‘granny’s scared of the thunder’. It’s only way we can really describe it.” Yousaf is having regular conversation with the Foreign Office, although Cleverly has yet to respond directly to a letter Yousaf sent on Tuesday urging him to push for a humanitarian corridor. “I don’t know anyone that suggests Israel doesn’t have the right to protect itself from terror. Those scenes that we witnessed on Saturday morning were horrific and there’s no equivocation about the fact that they are to be condemned in the strongest possible way,” said the SNP leader. “For me, though, that cannot be a justification for the collective punishment of 2.2 million people. If you cut off electricity, food, fuel, medical supplies, then it doesn’t just harm Hamas, it harms all of those innocent civilians.” Yousaf pleaded with the international community to remember the “ordinary human beings” caught up in the conflict. “We can talk for hours about the geopolitical situation, the two-state solution and 1967 borders, but if we strip it back to the most basic humanity we have many people – particularly in our Jewish community – who do not know if their family members are alive or not. “And we have those in Gaza who do not know if their family is going to survive an hour longer, and they have nothing to do with geopolitics, they are just ordinary human beings”. A few minutes after speaking to the Guardian, during another interview, Yousaf was interrupted by his wife who entered the room crying and telling him she could not contact her family. The first minister later explained that his wife had recognised from a TV report that a neighbourhood close to where her family were staying had been hit. “But … thank God, her mum has got a message through saying: ‘Our neighbourhood is being hit, we haven’t been hit yet,’” he said. “The Israeli government know where our family is, they know the coordinates … so my hope is that they won’t be hit.”