The United Nations said that the Israeli military has given 24 hours for about 11 lakh Palestinians to move towards the southern part of Gaza.
The UN expressed worry as the order signalled that Israel is preparing for a ground offensive.
Calling the order "impossible", UN spokesman Stephane Dujarric appealed that any such order must be rescinded as it could transform what is already a tragedy into a calamitous situation.
"The United Nations considers it impossible for such a movement to take place without devastating humanitarian consequences," Dujarric said in a statement.
"The United Nations strongly appeals for any such order, if confirmed, to be rescinded avoiding what could transform what is already a tragedy into a calamitous situation," he added.
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