A panel of independent United Nations experts issued a statement on Thursday, denouncing acts of violence against civilians in Israel and expressing strong disapproval of retaliatory strikes on Gaza that result in "collective punishment.
While condemning the "horrific crimes committed by Hamas", the group said that Israel had resorted to "indiscriminate military attacks against the already exhausted Palestinian people of Gaza".
"They have lived under unlawful blockade for 16 years, and already gone through five major brutal wars, which remain unaccounted for," the group, which includes several UN special rapporteurs, said in a statement.
"This amounts to collective punishment. There is no justification for violence that indiscriminately targets innocent civilians, whether by Hamas or Israeli forces. This is absolutely prohibited under international law and amounts to a war crime."
The group said that taking hostages in the context of hostilities also constituted a war crime.
"The civilians taken by Hamas must be immediately released, pending which their fate and whereabouts must be disclosed," the experts said.
The Israeli death toll has risen to more than 1,300 people since Saturday. Most were civilians gunned down by Hamas in their homes, on the streets or at a dance party.
Scores of Israeli and foreign hostages were taken back to Gaza.
Israel said on Thursday there would be no humanitarian break to its siege of the Gaza Strip until all its hostages were freed.
