A senior UN official, Louise Arbour, has expressed alarm at the magnitude of violence committed by both sides in the Gaza Strip and Israel.
Arbour called on those who killed civilians to be made accountable
The High Commissioner for Human Rights also criticised Israel's "disproportionate use of force".
She said the protection of civilian lives and human rights "cannot await the outcome of a political process".
On Monday Israel ended a major offensive in which more than 120 Palestinians were killed.
The Israelis say the incursion was aimed at stopping rocket fire into Israel by Palestinian militants.
Two Israeli soldiers and an Israeli civilian were also killed over roughly the same period.
Speaking at a session of the UN's Human Rights Council, Ms Arbour called on Israeli and Palestinian authorities to investigate civilian killings and to make sure perpetrators were held accountable.
"I repeat my condemnation of the rocket attacks by Palestinian militants against Israeli civilian targets, as well as of the Israel Defence Forces' disproportionate use of force," she said.
At the council session Pakistan submitted a resolution on behalf of the Organisation of the Islamic Conference calling for an "immediate cessation of all Israeli military attacks throughout the occupied Palestinian territory and the firing of crude rockets by Palestinian combatants".
The UN Security Council on Sunday condemned the violence in Gaza.
The council had been due to hear a report by UN special rapporteur John Dugard on the human rights situation in the occupied territories. This was delayed due to scheduling problems until the council's next session in June.
In the report, which was put on the council's website last week, Mr Dugard argues that acts of terrorism committed by Palestinians are an "inevitable consequence" of the Israeli occupation.
"While such acts cannot be justified, they must be understood as being a painful but inevitable consequence of colonialism, apartheid or occupation," Mr Dugard writes.
He argues that a distinction must also be made between what the report calls the mindless terror of al-Qaeda and acts committed in a war against military occupation.
The report says violence will continue as long as Israel occupies Palestinian land, and that Israel cannot, therefore, set peace as a precondition for ending its occupation.
Israel has rejected the report as biased.