MADRID, Spain - Israel has broken international law with its "relentless" bombardment of Gaza that has levelled neighbourhoods and killed thousands of Palestinians, a UN rights expert said Thursday.

The comments by Francesca Albanese, an Italian lawyer who is the UN special rapporteur on the Palestinian territories, came as Israel confronts a case brought by South Africa to the UN's International Court of Justice accusing it of genocide.

"Israel has done a number of things that are highly illegal, highly unlawful," Albanese told a Madrid news conference.

While Israel has the right to self-defence, international humanitarian law must be respected "to protect people who are not actively involved in combat. Civilians, prisoners of war and the sick and wounded," she added.

This meant distinguishing between combatants and civilians and ensuring military attacks are proportionate to avoid excessive harm to civilians, Albanese said.

"Instead what has happened is over 100 days of relentless bombing  -- the first two weeks using 6,000 bombs per week, bombs of 2,000 pounds, in highly crowded area." she said.

"Most hospitals have been made dysfunctional. A good number of them, the major ones, have been closed, bombed or taken over by the army. People are dying now not only because of the bombs but because there is not sufficient health infrastructure to cure them of wounds.

"The number of kids who get amputated every day is shocking, one or two limbs. During the first two months of this (war) 1,000 kids were amputated without anaesthesia. It is a monstrosity," she added.

Fighting has ravaged the Palestinian territory since Hamas fighters launched an attack in southern Israel that resulted in the death of about 1,140 people, mostly civilians, according to an AFP tally based on official Israeli figures.

Israel has responded with a relentless bombardment and a ground offensive, killing at least 24,620 Palestinians, around 70 percent of them women, children and adolescents, according to Gaza health ministry figures.

Special Rapporteurs are not UN staff but are independent experts named by the UN human rights commission who monitor rights areas.

Albanese said she "firmly condemned" the violence carried out by Hamas, which she said amounted to war crimes and may also be crimes against humanity, but "nothing justifies what Israel has done".

South Africa took its case to the International Court of Justice last week. But it has been fiercely resisted by Israel with support from the United States and other allies.

Israel has insisted its military response was in self-defence after the brutality of the Hamas attacks and that the genocide case is "distorted".

It's representatives have highlighted how the  militants also seized about 250 captives on October 7. Israel says 132 remain in Gaza, including at least 25 believed to have been killed.