Israeli forces have been intensifying their attacks in the northern Gaza Strip to eliminate Hamas militants, causing many casualties.
Local media in Gaza reported that Israeli strikes from late Saturday to Sunday on houses and a school sheltering many civilians killed at least 69 people.
United Nations Secretary-General Antonio Guterres said in a statement on Sunday that he is shocked by the harrowing levels of death, injury and destruction in northern Gaza.
He repeated his appeal for an immediate ceasefire, saying that the plight of Palestinian civilians trapped in the north is unbearable.
Meanwhile, Israeli media report that the head of the Mossad intelligence agency traveled to Qatar on Sunday for talks with the director of the CIA on a ceasefire and the return of hostages.
A Saudi Arabian TV station reported on Sunday that Hamas presented negotiators with a deal for an immediate end to the fighting, a withdrawal of Israeli troops from Gaza, and the exchange of a certain number of Palestinian detainees in return for the release of all Israeli hostages at once.