Deadly strikes were reported early Saturday in Rafah - the overcrowded Gaza border town dubbed a "pressure cooker of despair" by the UN - as international mediators readied a new push to seal a tentative truce deal between Israel and Hamas.
Hundreds of thousands of displaced Palestinians have fled south to Rafah since the outbreak of the war.
The city was formerly home to 200,000 inhabitants. Now, more than half of Gaza's two million-plus population are living there, a WHO representative said Friday.
"Most are living in makeshift structures, tents or out in the open," OCHA spokesman Jens Laerke said during a briefing in Geneva.
The health ministry in Gaza said more than 100 people in total were killed across the territory overnight, as the war in the coastal enclave fast approaches the four-month mark.
More than 27,000 people have been killed in Gaza since Israel launched its war on the Palestinian territory on 7 October.