Israel's repeated use of heavy bombs in the densely-populated Gaza Strip indicates repeated violations of the laws of war, the UN said Wednesday, highlighting six attacks that killed at least 218 people.

In a fresh report, immediately slammed by Israel as deeply biased, the United Nations rights office provided details on the six attacks, which it said were emblematic of a concerning pattern.

They involved the suspected use of up to 2,000-pound bombs on residential buildings, a school, refugee camps and a market.

The rights office, known by the acronym OHCHR, said it had verified 218 deaths in those attacks, which were carried out in the early months of the war on October 7, but said it had information indicating the number of fatalities "could be much higher".

"The requirement to select means and methods of warfare that avoid or at the very least minimise to every extent civilian harm appears to have been consistently violated in Israel's bombing campaign," UN rights chief Volker Turk said in a statement.

The report concludes that the series of Israeli strikes, exemplified by the six attacks carried out between October 9 and December 2, suggested that Israel's military had "repeatedly violated fundamental principles of the laws of war", the statement said.

- 'Collapse tall structures' -

Gaza's deadliest war was sparked by Hamas's unprecedented attack inside Israel on October 7, which resulted in the deaths of 1,194 people, mostly civilians, according to a tally based on Israeli official figures.

The militants also seized 251 hostages. Of these, 116 remain in Gaza, although the army says 41 are dead.

Israel's retaliatory offensive has killed at least 37,372 people in Gaza, also mostly civilians, according to the territory's health ministry.

Among the attacks listed in Wednesday's report were the strikes on Ash Shujaiyeh neighbourhood, in Gaza City on December 2 last year.

It caused destruction across an approximate diagonal span of 130 metres (420 feet), destroying 15 buildings and damaging at least 14 others, it said.

The extent of the damage and the craters visible and seen on satellite imagery indicated that around nine 2,000-pound GBU-31 bombs were used, it said, adding that it had received information that at least 60 people were killed.

GBU-31s, along with 1,000-pound GBU-32s and 250-pound GBU-39s "are mostly used to penetrate through several floors of concrete and can completely collapse tall structures," UN rights office spokesman Jeremy Laurence told reporters.

"Given how densely populated the areas targeted were, the use of an explosive weapon with such wide area effects is highly likely to amount to our prohibited indiscriminate attack."

- 'Crimes against humanity'? -
Ajith Sunghay, head of OHCHR's office in the Palestinian territories, said that the report focused heavily on Israeli actions, since the weapons used by Israel's military were far more destructive.

The missiles fired by Hamas, while "absolutely unacceptable", he said, "have not caused significant killing during the war" by comparison.

The incidents detailed in the report did not include a key and controversial blast early in the war on Gaza's Al-Ahli hospital compound, where Hamas initially talked about hundreds killed in what they said was an Israeli strike.

Israel denied responsibility and blamed a misfired rocket launched by Islamic Jihad militants -- a claim backed by the US -- while Western intelligence sources suggested a far lower death toll.

Asked why this incident did not figure on the list, Sunghay suggested the team had not had enough information to include it.

The report highlighted that unlawful targeting was not only a violation of the laws of war.

When committed as part of a widespread or systematic attack against a civilian population, in line with an official state or organisational policy, it "may also implicate crimes against humanity", it said.

Israel harshly criticised the report, suggesting it aimed to "lambast and single-out Israel, while further shielding Hamas terrorists in Gaza".

"OHCHR has been echoing Hamas narrative and spreading unfounded allegations," Meirav Eilon Shahar, Israel's ambassador in Geneva, said in a statement.

"This report shows the deep-rooted bias against Israel that has existed in OHCHR for decades," she added.