Volker Turk said at least 505 Palestinians had been killed in the West Bank by the Israeli military and by West Bank settlers since the war in nearby Gaza erupted nearly eight months ago.
Palestinian officials have given a toll of at least 523.
Two dozen Israelis, including eight soldiers, have also been killed in West Bank clashes or alleged attacks by Palestinians from the West Bank during the same period, he said.
“As if the tragic events in Israel and then Gaza over the past eight months were not enough, the people of the occupied West Bank are also being subjected to day-after-day of unprecedented bloodshed,” he said in a statement.
“It is unfathomable that so many lives have been taken in such a wanton fashion.”
Turk insisted “the killing, destruction and widespread human rights violations are unacceptable, and must cease immediately”.
“Israel must not only adopt but enforce rules of engagement that are fully in line with applicable human rights norms and standards,” he said, demanding accountability for all alleged unlawful killings.