Forced displacement has pushed over a million people away from the Gazan city of Rafah, the United Nations Palestinian Refugee Agency (UNRWA) said on Monday.
The small city on the southern edge of the Gaza Strip had been sheltering around 1 million Palestinians who fled Israeli operations on other parts of the enclave, aid groups said.
Since early May, the IDF has been carrying out what it says is a limited operation in Rafah to root out Hamas fighters and dismantle infrastructure used by the Palestinian terrorist organization that runs Gaza.
Thousands flee to Khan Yunis
The IDF has told civilians to go to an "expanded humanitarian zone" about 20 km (12 miles) away.
Many Palestinians have complained they are vulnerable to Israeli operations wherever they go and have been moving up and down the Gaza Strip in the past few months.
UNRWA said thousands of families now shelter in damaged and destroyed facilities in the city of Khan Yunis, where the agency is providing essential services despite "increasing challenges."
"Conditions are unspeakable," the agency added.