"The council cannot disavow its collective responsibility. It cannot continue to fiddle while Gaza burns."
Ryad Mansour, the Palestinian observer at the UN, called for an independent investigation of Israel's "grave breaches and systematic violations of international law".
"Since this crisis began, it is without a doubt that a multitude of war crimes have been perpetrated by the occupying power [Israel]," he said while also calling for "measures for the protection of the defenceless Palestinian civilian population."
Gabriela Shalev, the Israeli ambassador to the UN, dismissed the session as a "cynical, hateful and politicised [attempt] to de-legitimize Israel's fundamental right to defend its citizens".
Gaza war 'genocide'
The emergency meeting had been requested by the 118-member UN member states making up the non-aligned movement.
An Israeli delegate had sought to block the session on procedural grounds by arguing that under the UN charter the 192-member assembly could not rule on a matter already being tackled by the Security Council, but the move was dismissed.
D'Escoto noted that the Security Council last week had called for a Gaza ceasefire leading to the withdrawal of Israeli forces.
"Prime Minister Olmert's recent statement disavowing the authority of Resolution 1860 [the Security Council resolution] clearly places Israel as a state in contempt of international law and the United Nations," d'Escoto added.
He urged the assembly to agree its own non-binding assembly resolution reflecting "the urgency of our commitment to end this slaughter" in Gaza.
Israel has continued its offensive regardless of the resolution which was also rejected by Hamas.
D'Escoto, a former Nicaraguan foreign minister, told Al Jazeera on Tuesday that Israel's killings of Palestinians in Gaza amounted to "genocide".
Almost 1,100 Palestinians have been killed during Israel's Gaza offensive, which Israel says is to stop Palestinian rocketfire coming from Gaza.