The war in Gaza has "ruptured any sense of a shared humanity," the head of the International Committee of the Red Cross said on Saturday.
ICRC head Mirjana Spoljaric called for an urgent ceasefire in Gaza, saying Israel and Hamas must respect international law and protect civilians caught up in their conflict.
She said getting a steady, substantial flow of desperately needed aid into the besieged Palestinian territory - where the United Nations says more than 90 percent of the population is on the brink of famine - was "only part of the solution".
"Alleviating the humanitarian catastrophe in Gaza starts with a clear will and measures that safeguard civilian life and human dignity, meaning both sides must conduct their military operations in a way that spares the civilians who are caught in the middle," Spoljaric said.
"The only way to achieve this is that the parties strictly adhere to international humanitarian law, which means preserving the life, dignity and humanity of all people affected by armed conflict, regardless of which side they are on.
"It is the line between humanity and barbarity," she insisted.
"Preserving civilian life and health is the rule, not the exception."
Israel has waged a relentless ground and air offensive in the Gaza Strip which has killed over 30,000 people, mostly women and children.
Many of Israel's atrocities have been described as akin to war crimes and genocide.
Five months into the war, an international effort is gathering pace to get humanitarian relief into the densely populated enclave by sea, in a bid to counter restrictions on access by land that have been blamed on Israel.
The UN says 2.2 million of Gaza's 2.4 million people are on the verge of famine and desperately short of drinking water.
"As an occupying power, Israel must provide for the basic needs of the population or facilitate the safe and unimpeded delivery of humanitarian relief," Spoljaric said.
The war had "ruptured any sense of a shared humanity", she said.
"The situation in the Gaza Strip degenerates by the hour. There is nowhere safe for people to go. The civilian death toll and the ongoing captivity of hostages are shocking and unacceptable," Spoljaric said.
"In the face of such deep suffering", the ICRC called urgently for a ceasefire to allow "a steady, robust flow of humanitarian aid" to reach people in Gaza.
It urged Hamas to release the hostages it was still holding, care for their safety and medical needs, and allow the ICRC to visit them.
It said the ICRC must be "notified" of any Palestinians detained by Israel and allowed to visit them, stressing Israel had a duty to treat them "humanely" and allow them to "communicate with family".
Spoljaric urged world leaders to make respect for international law a "political priority".