London - UN humanitarian chief Valerie Amos expressed deep concern on Thursday about the mounting civilian casualties in Gaza, warning that it was "almost impossible" for Palestinians to shelter from Israeli airstrikes.
"The reality in Gaza is, it doesn't matter how hard Israel tries to minimise harm, this is an extremely overcrowded stretch of land," Amos told BBC radio.
"Forty-four percent of that land has been declared a no-go zone by the Israeli army so there aren't that many places for people to go."
She described "people crowded into a sliver of land, almost impossible for them to move".
More than 700 Palestinians have been killed in Gaza in 17 days of conflict between Israel and Hamas.
The United Nations said on Wednesday that three quarters of those killed were civilians and one third of those were children - the equivalent of one child killed each hour over the previous two days.
"The trauma that they are experiencing is terrible, and one child killed every hour in the past two days - each and every one of us should sit up and take notice of this," said Amos.
The British peer, the UN's Under-Secretary-General for Humanitarian Affairs and Emergency Relief Co-ordinator, added her call for a ceasefire to end this "devastating situation".
"No one is denying the right of Israel to defend itself but there are huge concerns about the impact this is having on ordinary people on the ground," she said.
Situated on the Mediterranean coast, flanking Israel and Egypt, the Gaza Strip is home to 1.7 million Palestinians who live in an area stretching just 362 square kilometres, making it one of the most densely-populated territories on the planet.