A senior UN official has warned that half of Gaza's population is starving as fighting continues there.
Carl Skau, deputy director of the UN's World Food Programme, said only a fraction of the necessary supplies had made it into the strip and nine out of ten people could not eat each day.
Conditions in Gaza have made supplies "almost impossible," Skau said.
Israel says it must continue airstrikes on Gaza to eliminate Hamas and return Israeli hostages home.
Israel Defense Forces spokesman Lt. Col. Richard Hecht told the BBC that "any death and pain of a civilian is painful, but we have no alternative."
"We are doing everything we can to get into the Gaza Strip as much as possible," he said.
The Hamas-run Health Ministry claims Israel has killed more than 17,700 Gazans during its retaliatory campaign, including more than 7,000 children.
International pressure and a temporary seven-day ceasefire last month allowed some much-needed aid to enter the Gaza Strip, but the World Food Program insists a second border crossing is now needed to meet demand.
According to Skau, nine out of ten families in some areas spend "a whole day and night without any food".
People in Khan Younis in southern Gaza, a town now surrounded by two fronts of Israeli tanks, say the situation there is dire.
Dr Ahmed Moghrabi, head of plastic surgery and burns at the city's only remaining health facility, Nasser Hospital, fought back tears as he spoke to the BBC about the lack of food.
"I have a three-year-old daughter, she always asks me for some sweets, apples, fruits. I can't provide them. I feel helpless," he says.
"There is not enough food, only rice, only rice, can you believe it
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