The head of the World Health Organisation on Saturday appealed to Israel "in the name of humanity" not to launch an assault on Rafah, where most of Gaza's population is sheltering.
"I'm gravely concerned about reports of an Israeli plan to proceed with a ground assault on Rafah," WHO chief Tedros Adhanom Ghebreyesus wrote on X, formerly Twitter.
"Further escalation of violence in this densely populated area would lead to many more deaths and suffering," he added.
"In the name of humanity, we appeal to Israel not to proceed and instead to work towards peace."
An evacuation planned by the Israeli army ahead of launching its assault was not a practical solution, he argued.
"The 1.2 million people in Rafah do not have anywhere safe to move to.
"There are no fully functional, safe health facilities that they can reach elsewhere in Gaza," he said. "Many people are too fragile, hungry and sick to be moved again...
"This humanitarian catastrophe must not be allowed to worsen."
Prime Minister Benjamin Netanyahu approved the military's "plans for action in Rafah", according to a statement Friday, which gave no details or a timeline.
The United Nations and the United States have also repeatedly warned against such a military operation.
Netanyahu has for weeks vowed to continue the war, having promised to destroy Hamas in the wake of the October 7 attack by Islamist militants.
The Hamas attack resulted in about 1,160 deaths in Israel, mostly civilians, according to an AFP tally of official figures.
Israel has carried out relentless bombardment and a ground invasion in response that has killed at least 31,553 people in Gaza, most of them women and children, according to the health ministry.
