The UN human rights chief on Friday backed calls for an international investigation into Israel's use of deadly force against protesters on the Gaza border, which he described as "wholly disproportionate".
Addressing a special session of the UN Human Rights Council on the violence which has claimed more than 100 Gazan lives in six weeks, Zeid Ra'ad Al Hussein warned that "killing resulting from the unlawful use of force by an occupying power may also constitute wilful killings, a grave breach of the Fourth Geneva Convention".
The protesters' "actions alone do not appear to constitute the imminent threat to life or deadly injury which could justify the use of lethal force", Mr Al Hussein said.
He said there was "little evidence" of Israeli claims that it made an effort to minimise casualties.
The special session will consider a resolution calling for an "independent, international commission of inquiry".
The Arab League also called for an international investigation into the killings at an emergency meeting in Cairo on Thursday.
Speaking at that meeting, UAE Minister of State for Foreign Affairs Dr Anwar Gargash condemned the Israeli occupation's use of excessive force against unarmed Palestinians.
The majority of the deaths in Gaza - nearly 60 - came on Monday as Palestinians protested against the opening of the US embassy in Jerusalem.
"We warn against the negative repercussions of such a dangerous escalation and we call for international probe to hold those responsible for this massacre accountable," Dr Gargash said. "At the same time, we stress that the US decision to transfer the US Embassy to Jerusalem has complicated the situation."
The Minister of State for Foreign Affairs also called on the international community to stop the violence against Palestinians and end Israeli occupation of the Palestinian Territories, state news agency Wam reported.
"We also slam the use of the veto by the US to undermine the Security Council from carrying out its duty to achieve a transparent and impartial probe towards the massacres committed by Israel against the Palestinian people. We stress that there is no security in the region without a just, permanent and comprehensive solution of the Palestinian cause based on the two-state solution," Dr Gargash said.
Friday's special session of the UN Human Rights Council came at the request of Palestine and the UAE, on behalf of Arab countries in the council. It will discuss a draft resolution presented by Pakistan on behalf of the Organisation of Islamic Cooperation (OIC) and backed by 47 UN member states, which calls for investigators to look into "all violations of international humanitarian law and international human rights law ... in the context of the military assaults on large scale civilian protests that began on 30 March 2018".
It said the aim should be to "establish the facts and circumstances" around "alleged violations and abuses including those that may amount to war crimes and to identify those responsible".
In addition to the Arab countries, China, France, Brazil, Sweden, and Switzerland were among the 51 countries who supported the special session.
Meanwhile, Kuwait is urging the Security Council to condemn Israel's use of force against Palestinian civilians "in the strongest terms," especially in the Gaza Strip, and to deploy and international force to protect civilians.
A draft resolution circulated by Kuwait, the current Arab representative on the council, also demands that Israel "immediately cease its military reprisals, collective punishment and unlawful use of force against civilians, including in the Gaza Strip".
It calls for measures to guarantee the safety of Palestinian civilians, including the deployment of "an international protection mission".
The United States has defended Israel's actions in Gaza and will very likely veto the resolution if it is put to a vote.
The US earlier blocked Kuwait's attempt to get the Security Council to issue a condemnation of Israel's killing of protesters on Monday, saying it was one-sided and failed to mention incitement of violence by Hamas, the Islamic militant group that rules Gaza.