Almost 40 Palestinian children have been killed so far this year in the occupied territories with Israeli forces appearing to use lethal force in a manner that violates international human rights law, the United Nations rights chief Michelle Bachelet said in the statement.
"Inflicting hurt on any child during the course of conflict is deeply disturbing, and the killing and maiming of so many children this year is unconscionable," Bachelet added.
Nineteen Palestinian children were killed in occupied Palestinian territory in the last week alone, bringing the death toll of children since the start of the year to 37, according to the statement.
Seventeen of the children were killed during last weekend's attacks on Gaza by Israeli forces, and two more were killed on Tuesday in Israeli operations in the occupied West Bank.
The toll of civilian casualties in the Israeli attack on Gaza "was heavy", the UN rights chief said.
"International humanitarian law is clear. Launching an attack which may be expected to incidentally kill or injure civilians, or damage civilian objects, in disproportionate manner to the concrete and direct military advantage anticipated, is prohibited. Such attacks must stop," Bachelet said.
The UN human rights office has confirmed that among the 48 Palestinians killed in the three-day onslaught on Gaza from Friday to Sunday, at least 17 were children and four were women.
Nearly two-thirds of the 360 Palestinians reported injured in the Israeli offensive were civilians, including 151 children and 58 women, the UN said.