More than one million Palestinians are crammed into Rafah at the southern tip of the Gaza Strip, on the border with Egypt. Many are living in tent camps and makeshift shelters after fleeing Israeli bombardments elsewhere in Gaza.
The Israeli military says it wants to flush out Islamist militants from hideouts in Rafah and free hostages being held there after the Hamas rampage in Israel on Oct. 7, but has given no details of a proposed plan to evacuate civilians.
Israeli Prime Minister Benjamin Netanyahu, who faces growing international pressure to hold off on the planned assault, has given no indication as to when the offensive might take place.
"The possibility of a military operation in Rafah, with the possibility of the (border) crossing closing down, with the possibility of spillover... a sort of Egyptian nightmare ...is one that is right before our eyes," Martin Griffiths told diplomats at the United Nations in Geneva.
He said the notion that the people of Gaza could evacuate to a safe place was an "illusion".
"We must all hope that friends of Israel and those who care about Israel's security give them good counsel at this moment," Griffiths said.
The United Nations has said an Israeli offensive on Rafah could "lead to a slaughter".
Speaking at the same meeting as Griffiths, Mirjana Spoljaric, head of the International Committee of the Red Cross (ICRC), said the absence of a clear evacuation plan, including for the sick and elderly, would bring suffering to a new level.
"The suffering on both sides, the carnage we have seen since the 7th of October will reach unimaginable depths if operations on Rafah are intensified the way they have been announced," Spoljaric said.
(Reporting by Gabrielle Tétrault-Farber and Emma Farge; Editing by Bartosz Dabrowski, Timothy Heritage and Andrew Heavens)
