"The simplest truth is that a ground operation in Rafah will be nothing short of a tragedy beyond words. No humanitarian plan can counter that," Griffiths said in a statement on Tuesday.
He said more than 1.2 million people were seeking refuge in Rafah after fleeing from Israeli bombardments in the north of Gaza.
His remarks came after Israeli premier Benjamin Netanyahu vowed to launch an offensive on Rafah.
"The idea that we will stop the war before achieving all its objectives is out of the question," the head of the Israeli regime said on Tuesday, according to a statement from his office.
Earlier the UN chief urged Israel against invading Rafah, calling it an intolerable escalation.
“All members of the Security Council, and many other governments, have clearly expressed their opposition to such an operation. I appeal for all those with influence over Israel to do everything in their power to prevent it,” he said.
Guterres said any such incursion would have a devastating impact on Palestinian lives in Gaza and across the occupied territories.
He also called on Israel’s allies to pressure the regime to cancel its invasion plan.
Rafah has turned into a tent city since Israel started its genocidal campaign in early October.
The Palestinian city is currently hosting one and a half million displaced people from across the besieged territory.
Israel began its brutal onslaught on October 7.
Israel, which currently faces genocidal crimes at the International Court of Justice (ICJ), has killed 34,500 Palestinians since last October when it waged a bloody war on the Gaza Strip.
Over 77,643 other Palestinians have also been injured, and around 8,400 may be trapped under rubble.
AMK/PressTV