A U.N. spokesman said such a movement would turn “what is already a tragedy into a calamitous situation.”

Israel’s military has informed the United Nations that the entire population of northern Gaza should relocate to the southern half of the territory within 24 hours, the U.N. spokesman, Stéphane Dujarric, said late on Thursday night, adding that such a movement — involving over one million people — would lead to “devastating humanitarian consequences.”

“The same order applied to all U.N. staff and those sheltered in U.N. facilities — including schools, health centers and clinics,” Mr. Dujarric said.

The U.N. was told that the marker dividing the north from south was Wadi Gaza, the statement said.

The U.N. Security Council is scheduled to hold an emergency meeting on Friday afternoon in a closed consultation format