Northern and central Gaza were hit by a second day of heavy Israeli airstrikes on Tuesday, attacks Hamas said threatened to derail new international efforts to broker a ceasefire and hostage release deal. Residents of Gaza City reported helicopter strikes, explosions and gun battles as Israel expanded its two-week-old offensive in Shuja’iya, an eastern neighbourhood, moving tanks into areas of the city where Hamas and Palestinian Islamic Jihad fighters have regrouped. More than 50 people had been killed in airstrikes on Gaza City and the central town of Deir al-Balah and surrounding refugee camps in the preceding 24 hours, medics said. A third round of leaflets dropped on several neighbourhoods told residents to evacuate to southern Gaza, leading to a new wave of displacement of people who were unable or unwilling to leave their homes when Israeli troops first entered the city at the end of October. In a statement, the Palestinian Red Crescent said all of its medical clinics in Gaza City had been forced offline. In Nuseirat camp, near Deir al-Balah, an Israeli airstrike in the early hours of Tuesday on a multistorey building killed 17 people, including 14 children, the Hamas media office said. Neighbours rushed to help medics and emergency workers recover bodies and search for survivors under the rubble. “They were displaced during the night after Al-Nuseirat camp school was hit … They said they would sleep in the house, fearing for the children, and there was a massacre in the house. They are not safe in the schools nor the houses,” Yasser Abu Hamada, a local resident, told Reuters. Witnesses said first responders had been unable to reach scores of bodies lying on the streets in Gaza City because of the ongoing fighting. The Israel Defense Forces (IDF) said in a statement that its forces were engaged in “close-quarter combat” in Gaza City and had killed more than 150 militants and destroyed tunnels and explosives in the past week. The last few days of airstrikes on the blockaded Palestinian territory are some of the fiercest since the war broke out after Hamas attacked southern Israel on 7 October. Hamas’s armed wing, the Izz ad-Din al-Qassam Brigades, described the fighting as “the most intense in months”. The new fighting has unfolded as international mediators make headway in ceasefire negotiations after a major concession from Hamas last week, when the group dropped its insistence on a “complete” ceasefire as a prerequisite for talks. Mediation efforts led by Egypt, Qatar and the US have since accelerated, with Egyptian media reporting that talks are due to continue in Doha and Cairo this week, attended by the CIA director, William Burns, and Israel’s Mossad chief, David Barnea. “There is an agreement over many points,” a senior source told al-Qahera news on Tuesday. But speaking on Monday night, the group’s Qatar-based political chief, Ismail Haniyeh, said that the “catastrophic consequences” of the latest battles on the ground in Gaza could “reset the negotiation process to square one”. The group has also accused Israel’s prime minister, Benjamin Netanyahu, of deliberately trying to thwart the truce talks.