The United Nations Security Council has scheduled an emergency meeting on Sunday morning in New York.
Health officials said that 11 Palestinians seeking aid were shot dead, and 11 adults died of malnutrition-related causes in the past 24 hours.
US special envoy Steve Witkoff was expected to meet with Qatar's prime minister in Spain on Saturday to discuss a new proposal to end the war, according to two officials familiar with the talks, who spoke on condition of anonymity.
Mediators Egypt and Qatar are preparing a new ceasefire framework that would include the release of all hostages — dead and alive — in one go in return for the war's end and the withdrawal of Israeli forces, two Arab officials have told The Associated Press.
Families of hostages were rallying again on Saturday evening to pressure the government of Prime Minister Benjamin Netanyahu.
There are fears for the fate of the 50 remaining hostages, with 20 of them thought to be alive and struggling.
"The living will be murdered and the fallen will be lost forever," if the offensive goes ahead, said Einav Zangauker, whose son Matan is held in Gaza.
A joint statement by nine countries, including Germany, Britain, France and Canada, said that they "strongly reject" Israel's decision for the large-scale military operation, saying it will worsen the "catastrophic humanitarian situation," endanger hostages and further risk mass displacement.
A separate statement by more than 20 countries, including ceasefire mediators Egypt and Qatar, along with Saudi Arabia, Turkey and the United Arab Emirates, called Israel's decision a "dangerous and unacceptable escalation".
Meanwhile, Russia said Israel's plan will aggravate the "already extremely dramatic situation" in Gaza.
And Germany has said it won't authorise any exports of military equipment to Israel that could be used in Gaza until further notice.
Officials at Nasser and Awda hospitals said that Israeli forces killed at least 11 people seeking aid in southern and central Gaza.
Some had been waiting for aid trucks, while others had been approaching aid distribution points.
Israel's military denied opening fire and said that it was unaware of the incidents.
The military secures routes leading to distribution sites run by the Israeli-backed and US-supported Gaza Humanitarian Foundation, which didn't immediately respond to a request for comment.
Two witnesses told the AP that Israeli troops fired toward crowds approaching a GHF distribution site on foot in the Netzarim corridor, a military zone that bisects Gaza.
One witness, Ramadan Gaber, said that snipers and tanks fired on aid-seekers, forcing them to retreat.
In Deir al-Balah in central Gaza, some aid-seekers cheered the latest airdrops of aid.
Hundreds of people rushed to grab what they could, though many have called the process degrading.
Aid organisations have called airdrops expensive, insufficient and potentially dangerous for people on the ground.
Israel's military said that at least 106 packages of aid were airdropped on Saturday as Italy and Greece joined the multi-country effort for the first time.
Footage from Italy's defence ministry showed not only packages being parachuted over Gaza but the dry and devastated landscape below.
"This way is not for humans, it is for animals," said one man at the scene, Mahmoud Hawila, who said he was stabbed while trying to secure an airdropped package.
Barefoot children collected rice, pasta and lentils that had spilled from packages onto the ground.
