International Criminal Court prosecutor Karim Khan said Sunday preventing access to humanitarian could be a crime, after visiting Egypt's Rafah crossing with Gaza, the main entry point for international aid.
"Impeding relief supplies as provided by the Geneva conventions may constitute a crime within the court jurisdiction," Khan told reporters in Cairo.
He said he wanted "to underline clearly to Israel that there must be discernible efforts without further delay to make sure civilians" in the Gaza Strip "receive basic food, medicines".
"I saw trucks full of goods full of humanitarian assistance stuck where nobody needs them, stuck in Egypt, stuck at Rafah," Khan said.
"These supplies must get to the civilians of Gaza without delay."
On Sunday the United Nations warned it feared a breakdown of public order after looting at food aid centres in Gaza run by its agency for Palestinian refugees, UNRWA.
UN chief Antonio Guterres said the situation was "growing more desperate by the hour" as casualties in the war increase and essential supplies of food, water, medicine and shelter dwindle.
People in the Palestinian territory have lived under Israeli blockade for 16 years and under complete siege for the past three weeks after the territory's Hamas rulers launched deadly attacks into Israel that sparked a war.
Hamas assaulted southern Israel on 7 October in the deadliest attack in Israel's history, killing 1,400 people, mostly civilians, and kidnapping 239 others, according to Israeli officials.
The health ministry in Gaza says the retaliatory Israeli bombardment has killed 8,005 people including 3,324 children.
Khan said his office had an ongoing investigation into "any crimes committed on the territory of Palestine and any crimes committed, whether it's by Israel and Palestine or whether it's acts committed on the territory of Palestine or from Palestine into Israel."
"This includes current events in Gaza and also current events in the West Bank," Khan said, adding that he was "very concerned also by the spike of the number of reported incidents of attack by settlers against Palestinian civilians" in the territory Israel has occupied since 1967.
Khan also said hostage taking was a breach of the Geneva Conventions.
"I call for the immediate release of all hostages taken from Israel and for their safe return to their families," Khan said.
The British lawyer said "Israel has clear obligations in relation to its war with Hamas, not just moral obligations but legal obligations" to comply with the laws of conflict.
"These principles equally apply to Hamas in relation to firing indiscriminate rockets into Israel," he said.