Israeli tank shelling and air strikes killed at least 39 Palestinians near Khan Younis after issuing new orders for people to leave some neighbourhoods in the area.
The Israeli army justified yet another instance of forced displacement of Palestinians on Monday due to what they said were renewed attacks from those areas.
To facilitate evacuations, the military said, it was adjusting the boundaries of a humanitarian zone in al-Mawasi west of Khan Younis to keep the civilian population away from areas of combat with Hamas-led Palestinian fighters.
The Palestinians, the United Nations and international relief agencies have said there is no safe place left in Gaza. Earlier in July, dozens of Palestinians were killed in separate Israeli attacks in the humanitarian-designated al-Mawasi area.
Health officials at Nasser Hospital in Khan Younis urged residents to donate blood because of the large number of casualties being rushed into the medical centre.
The Palestinian Civil Emergency Service said it had reports of dozens of people killed by Israeli aerial and tank fire on the eastern outskirts of Khan Younis but teams could not reach them because of the intensity of the bombardment.
Meanwhile, the Israeli military carried out air strikes on two houses in the Bureij and Deir el-Balah areas of the central Gaza Strip, wounding several people, medics said.
Another air strike in Gaza City in the north of the densely populated enclave killed two other Palestinians, they added.
A ceasefire effort led by Qatar and Egypt and backed by the United States has so far fallen short because of the Israeli hardline stance. Prime Minister Benjamin Netanyahu has refused to agree to a permanent ceasefire even if a deal is signed. Hamas has been demanding an end to the Israeli military operation as a condition for signing the deal.