He also said there were fears that the humanitarian situation would further deteriorate as the strip, home to 1.5 million people, was suffering from acute shortages of fuel, food and medical supplies.
Israeli leaders have maintained that there is no humanitarian crisis for the Palestinians living in the densely populated territory, and that they have been keeping border crossings open and are delivering vital supplies.
Several times last week, Tzipi Livni, the Israeli foreign minister, denied there was a humanitarian crisis.
She said in Paris on Saturday that Israel had been careful to protect civilians and there was no need for a humanitarian truce, since there was no humanitarian crisis.
Iyad Nasr of the Red Cross in Gaza City said Israel's offensive against Gaza had worsened the hardships created by the Israeli blockade over the last 18 months.
"The size of the operations and the size of the misery we are seeing here on the ground is just overwhelming," he said.