The mother of Mia Schem, a 21-year-old French-Israeli woman being held by Hamas, appealed for her release on Tuesday, calling her detention and that of an estimated 200 hostages “a crime against humanity”. Keren Schem told journalists in Jerusalem: “I didn’t know if she’s dead or alive until yesterday. All I knew is that she might be kidnapped. I’m begging the world to bring my baby back home. She only went to a party, to a festival party to have some fun. Now she’s in Gaza.” Hamas had released a video of Schem, who was taken hostage during the devastating attack on Israel. In the footage, Schem, whose injured arm is shown being treated by an unidentified medical worker, asks to be returned to her family as quickly as possible. On Tuesday, the French president, Emmanuel Macron, described the video as “an odious act”. The Elysée said Macron, who is on an official visit to Albania, demanded her unconditional release. “It is an ignominy to take innocent people hostage and put them on show in this odious way,” the presidential palace quoted Macron as saying. It added that France was “working with its partners to free French hostages held by Hamas”. Schem’s mother told the press conference: “This is a crime against humanity and we should all gather and stop this terror and bring everybody back home.” At least 199 Israelis and foreigners were seized by Hamas gunmen and taken captive in the attack on 7 October, which killed 1,300 people, the largest number of dead in a single day in Israel’s 75-year history. In the video, the first released by Hamas of a hostage allegedly speaking from captivity, Schem said she was being held in Gaza, was being well treated and appealed for her release. The US called on Hamas to immediately release all hostages, which include American citizens. “There should be no reason for them to have any hostages in the first place … we’re working very, very hard with our partners in the region to secure the release of all the hostages,” the US national security council spokesperson, John Kirby, told NBC. On Sunday, the French foreign minister, Catherine Colonna, met Schem’s family and the families of others killed or who were believed to have been taken hostage. The Israeli military issued a statement saying it was in constant touch with Schem’s family and condemning Hamas as a “murderous terrorist organisation”. It said it was using “all intelligence and operational measures” for the return of the captives. “In the video, Hamas is trying to portray itself as a humane organisation, while it is responsible for the murder and abduction of babies, women, children, and elderly,” it said. In the 78-second video, which was broadcast on Hamas’s Telegram channel, Schem says she is in Gaza, is being given medicine and wants to go home. It is unclear when it was filmed and if she was under duress during filming. Analysis by the New York Times suggests parts of it were filmed six days ago. Schem was abducted on 7 October from the Supernova music festival, where hundreds were killed. The Israeli military said her family was told of her abduction last week. Officials dismissed the video as propaganda designed to make Hamas appear humane. Schem’s family told Israeli media of their joy at seeing the video, with Schem’s aunt, named as Galit, calling it “a very significant step”. “She looks hurt and scared – but at least she’s alive,” she is quoted as saying. Earlier, Khaled Meshaal, a former Hamas chief who heads its diaspora office in Doha, spoke to AlAraby TV and said Hamas would spare no effort in using its captives as leverage to free 6,000 Palestinians held in Israeli prisons.