Britain accused Israel of inflicted the “grimmest captivity on the planet” on millions of Gazans with many people “starving”.
Foreign Secretary David Lammy warned of fresh sanctions against Israel unless it allows in more aid into the besieged strip and moves to end the war.
He also accused terror group Hamas of “exploting the chaos” in Gaza, using people as “human shields” and refusing to release hostages seized in Israel.
“The British government has no truck with Hamas and their behaviours,” he told Sky News.
“But it is right to say also that Israel controls what goes in and what comes out, it controls the Gaza strip.
“It’s got over two million people in 15 per cent of the Gaza strip, that is higher density than anywhere else on the planet, and the circumstances of that captivity are the grimmest on the planet and it’s for that reason that the international community is speaking out.”
He stressed that the “density now of Gaza is higher than any prison in the world”.
Earlier, Mr Lammy told Times Radio: “We see many, many people starving.
“We see many who are malnourished.
“We all understand deep concerns that hunger and food is being used as a weapon in this conflict.
“It will be the for courts to determine whether that is a breach of international humanitarian law.”
He added: “It’s entirely unacceptable for children to be in quite the need that they are in and certainly for children to be shot and killed as they wait for food.”
He stressed that he had warned Israel not to cut 400 aid points, and the work of the United Nations and its organisation in Gaza, to just four aid points.
Mr Lammy said he suspended a large number of arms sales licences to Israel last September because of a “clear risk of a breach of international humanitarian law” and that more measures were being planned in coming days unless Israel changes course.
Earlier, he joined other foreign ministers in condemning the Israeli government for depriving Gazans “of human dignity” as they called on the war to “end now”.
They also described proposals to move 600,000 Palestinians to a so-called “humanitarian city” in Rafah as “completely unacceptable”.
The foreign ministers reiterated calls for the remaining people being held hostage by Hamas to be released and asked for “all parties to protect civilians and uphold the obligations of international humanitarian law”.
Israel rejected the multi-national appeal, saying it was “disconnected from reality”.
Earlier this month Israeli defence minister Israel Katz laid out plans for the “humanitarian city” in Rafah, Gaza’s most southern city which has been heavily damaged through the war.
He reportedly said that the military would initially move 600,000 Palestinians there, with the aim of eventually transferring the whole population to Rafah.
