About 8,500 others have been wounded during the offensives. The death toll now surpasses the about 1,400 Palestinians killed during the Gaza war of 2008-2009.
A 72-hour ceasefire between Israel and Hamas in the Gaza Strip collapsed Friday less than three hours after taking effect, with Israel accusing Hamas of abducting one of its soldiers after the start of the proposed truce.
The missing soldier was named as 23-year-old Lieutenant Hadar Goldin.
Israeli officials said Hamas fighters attacked Israeli troops during an operation to destroying a tunnel about 90 minutes after the start of the ceasefire at 8am (0500GMT). Two soldiers were killed in the raid, according to a military spokesman.
A Hamas spokesman, Moussa Abu Marzouq, said the incident took place an hour before the ceasefire went into effect.
The agreement for the cessation of hostilities had been announced overnight by UN Secretary-General Ban Ki-moon and Kerry. Israel had said it would continue to operate on Hamas' tunnel network even during the ceasefire.
As hopes of an imminent lull in the violence fizzled aid agencies sounded the alarm over the looming humanitarian disaster in Gaza.
"The crisis in Gaza is fast spiralling out of control with water supplies critically low and a public health crisis imminent," aid group Oxfam warned.
Andrew Gardiner, a senior official with the International Committee of the Red Cross, said that unless engineers were soon able to repair damaged water systems people could die of thirst or disease.
Gaza residents had ventured onto the streets during the first two hours of the ceasefire, in order to stock up on food, bury their dead, visit the wounded in hospital. Those displaced by bombardments tried to salvage belongings from the rubble of their destroyed homes.
But plans for engineers to fix damaged water supplies and electricity lines had to be canceled as the clashes resumed.
Outbreaks of scabies have been reported at some UN schools serving as shelters for the more than 250,000 displaced.
At least two shelters have been hit by shelling in the past week, killing and injuring dozens.
The UN is appealing for 369 million dollars in emergency aid for the densely-packed territory of 1.8 million people, half of which has been deemed unsafe for civilians.
NJF/NJF