A total of 87 people were killed or missing under the rubble after an Israeli attack on Saturday on northern Gaza's town of Beit Lahiya, with more than 40 wounded, the Palestinian enclave's health ministry said on Sunday.

The Israeli military has said it was investigating reports of the incident, which could be one of the highest casualty tolls in months. Earlier, it said a total of 73 reported by the Hamas media office appeared exaggerated given the nature of the munitions used in the strike, which it said hit a Hamas target.

Gaza's health ministry said rescue operations were being hindered by communications problems and by the Israeli military operation still going on around the area, close to the border line with Israel, the ministry said.

"Victims are still under the rubble and on the road and ambulance teams and civil emergency can't reach them," it said in a statement.

The strike, late on Saturday night, came two weeks into a major operation around the town of Jabalia, just to the south of Beit Lahiya, where Israeli troops backed with tanks have been trying to squeeze out remaining Hamas fighters.

"Horrifying scenes unfolding in Gaza, amidst conflict, relentless Israeli strikes & an ever-worsening humanitarian crisis. I condemn the continuing attacks on civilians," UN Middle East peace envoy Tor Wennesland posted on X.

"Hostages must be freed, displacement of Palestinians must cease, & civilians must be protected."

Evacuation orders, directing people south, have fuelled fears among many Palestinians that the operation is intended to clear them out of the northern part of Gaza in order to help ensure Israeli control of the area after the war.

Israel has denied any such plans, saying it is trying to protect civilians and separate them from Hamas fighters.

The military says it has killed scores of armed Palestinian fighters, located weapons, and dismantled a variety of military infrastructure during the operation in Jabalia, home to one of Gaza's eight historic refugee camps.

Residents in Jabalia said Israeli forces raided shelters housing displaced families and detained dozens of men.

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The death last week of Hamas leader Yahya Sinwar had drawn hopes of a possible opening up of moves to end the fighting in Gaza, more than a year after the Oct. 7, 2023 attack on southern Israel by Hamas-led gunmen who killed some 1,200 people and seized 251 hostages.

But the latest incident underscores how intense the conflict in Gaza still remains, even as Israel's main focus has shifted north to its operation against the Iran-backed Hezbollah militia in Lebanon.

U.S. intel suggests planned strike on Iran

The latest strikes came as the United States is investigating an unauthorized release of classified documents that assess Israel's plans to attack Iran, according to three U.S. officials. A fourth U.S. official said the documents appear to be legitimate.

The documents, attributed to the U.S. Geospatial Intelligence Agency and National Security Agency and marked top secret, indicate that Israel was moving military assets in place to conduct a military strike in response to Iran's ballistic missile attack on Oct. 1.

The U.S. officials spoke on the condition of anonymity because they were not authorized to discuss the matter publicly.

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More than 42,600 Palestinians have been killed during Israel's ground offensive, according to Palestinian health ministry figures, and thousands more are thought to be buried under the rubble. Much of the coastal enclave has been destroyed and most of its 2.3 million population has been displaced.

As the fighting has continued, health officials have reported stark shortages of food, fuel and medical supplies to treat patients in the three remaining hospitals still partially operating in the area.

Officials at the Kamal Adwan, Indonesian and Al-Awda hospitals said their facilities were besieged by Israeli forces, and at Kamal Adwan Hospital officials said the facility came under Israeli fire.

WATCH | Northern Gaza cut off from getting supplies since Oct. 1, UN says:

No food aid has entered northern Gaza since Oct. 1, UN says

UN deputy spokesperson Farhan Haq says the main crossings into northern Gaza have been closed and no food or other essential supplies have entered since Oct. 1. More than 400,000 people who remain in the north are under increasing pressure to move south, he said.