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Israel has handed over the bodies of 100 Palestinians to authorities in Gaza.
The remains had been taken from hospitals and cemeteries across Gaza and were in various states of decomposition, the Palestinian news agency Wafa said on Tuesday.
Bodies were repatriated through the Kerem Shalom border crossing and were buried in a mass grave in the southern city of Rafah.
Some had organs missing, Wafa claimed, citing medical sources.
Gaza's Health Ministry on Tuesday said the death toll from the war had risen to 26,751 after at least 128 people were killed overnight in heavy Israeli bombardment and ground combat across the coastal strip. The number of injured rose to 65,636, it added.
The war, which began on October 7 after militant Hamas fighters entered southern Israel from Gaza and killed about 1,200 people and took about 240 hostage, has devastated large areas of the Palestinian enclave and displaced the majority of the 2.3 million population, most of whom were forced to flee south.
"At least 700,000 cases of infectious and skin diseases, colds, diarrhoea and epidemic hepatitis have been recorded among the displaced in the strip," Dr Ashraf Al Qudra, spokesman for the Health Ministry, said in a statement.
"Overcrowding, lack of suitable shelter, unavailability of adequate food and beverages, and the absence of necessary medical care has exacerbated the health and humanitarian disaster for those displaced."
Dr Al Qudra accused Israeli forces of carrying out mass executions in the southern city of Khan Younis, besieging its hospitals and preventing the movement of ambulances to rescue the wounded.
With the offensive against Hamas now focused on southern Gaza, Israeli Defence Minister Yoav Gallant said late on Monday that some units were "moving up to the north and preparing for what's to come", in reference to the Israeli-Lebanese border.
Israel's military and Lebanon's Iran-backed Hezbollah militant group, a Hamas ally, have had near daily exchanges of fire since the Gaza war started.
More Palestinians head south
The Israeli army warned citizens of Gaza city living in Al Nasser, Sheikh Al Ridwan, Al Shati camp and Al Rimal areas to evacuate to the south towards Deir Al Balah in central Gaza.
Large numbers of Palestinians were seen leaving on Monday after Israeli tanks rolled into Gaza city and started to fire at inhabited areas as the air force launched strikes from above.
Roaa Al Gharbawi, a resident of Al Nasser, said her family decided to move after the Israeli warning, despite having only recently returned to their damaged home after fighting in the area had subsided.
"We spent a difficult night that can't be described; we heard the sound of the tanks when they went to Al Shifa Hospital," Ms Al Gharbawi told The National.
"After we settled in our homes and fixed what we could by closing the broken windows with plastic and planning how to bring water and cook our food, they forced us to evacuate again."
Ms Al Gharbawi said her family planned stay at a school run by the UN refugee agency, UNRWA, in Deir Al Balah but she was worried about keeping her children warm in the winter weather, as she was unable to bring along enough warm clothes and blankets.
"What else do we have to experience?" she said. "We are dying every single minute. We want the war to stop immediately."
Daood Al Shamali, who lives in Al Rimal, told The National he refused to leave his home and move south.
"Enough is enough; they destroyed our homes and obliterated our future," he said. "What else do they want?
"We are not going to leave Gaza and we refuse to be humiliated. We want the war to end as soon as possible."
