Israeli strikes on several homes in the northern Gaza Strip overnight left at least 87 people dead or missing, the territory’s health ministry said Sunday.

Forty other people were injured in the strikes on the town of Beit Lahiya, which was one of the first targets of the Israeli ground invasion nearly a year ago.

The strikes came as the United States investigates the unauthorized disclosure of classified documents assessing Israel’s plans to attack Iran, according to three U.S. officials. A fourth said the documents appeared legitimate.

The documents, attributed to the U.S. Geospatial-Intelligence Agency and the National Security Agency and marked “top secret,” indicate that Israel is building military capabilities to carry out a military attack in response to Iran’s October 1 ballistic missile attack.

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

The United States has urged Israel to push for a ceasefire in the Gaza Strip following the assassination of Hamas leader Yahya Sinwar earlier this week. However, neither Israel nor Hamas have shown renewed interest in such a deal after months of negotiations broke down in August.

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Iran backs Hamas and the militant group Hezbollah in Lebanon, where a year of escalating tensions erupted into all-out war last month. Israel sent ground troops into Lebanon in early October.

Click to play video: 'Israel-Hezbollah conflict: At least 5 dead in Beirut after 10 IDF airstrikes'

The Israeli military did not immediately comment on the strikes in Beit Lahiya. It said it “continues to operate throughout the Gaza Strip, with airstrikes and ground operations.”

The dead included two parents and their four children, as well as a woman, her son, her daughter-in-law and their four children, according to Raheem Kheder, a medic. He said the strike levelled a multi-story building and at least four neighbouring homes.

Mounir al-Bursh, director general of the Health Ministry, said the influx of wounded people following the strikes was worsening “an already catastrophic situation for the health care system” in the northern Gaza Strip, in a message posted on the social network X.

Internet connectivity was cut off in the northern Gaza Strip late Saturday and had not been restored by midday Sunday, making it difficult to gather information about the strikes.

For the past two weeks, Israel has been conducting a major operation in the Jabaliya urban refugee camp, also located in the northern Gaza Strip. The army claims to have launched the operation against Hamas militants who had gathered there.

The north has already suffered the heaviest destruction of the war and has been surrounded by Israeli forces since late last year, following Hamas’ deadly attack on Israel.

Israel ordered the entire population of the northern third of the Gaza Strip, including Gaza City, to evacuate to the south in the first weeks of the war, and reiterated those instructions earlier this month. Most of the population fled last year, but an estimated 400,000 people remain in the north.

Palestinians who fled the north at the start of the war are still not allowed to return.