A senior Israeli military intelligence official said Sunday there is a "heavy suspicion" that Hamas penetrated the army before the Oct. 7 attack.
"Nukhba terrorists had information on the IDF (army)'s most sensitive sites, including those within the army that are most classified," the officer told Israel Hayom newspaper.
He said the Palestinian group had intelligence that could not have been taken from drones or observation posts.
"We must determine how this information reached them. We are talking about details that IDF commanders don't talk about even to their closest friends," he added.
He said the leaked intelligence represents a "double failure" for the Shin Bet domestic security service, which is responsible for uncovering Hamas' plans and foiling its espionage attempts.
Israel has launched a deadly offensive on the Gaza Strip following the Oct. 7 attack, which Tel Aviv says killed nearly 1,200 people.
At least 28,176 Palestinians have since been killed and 67,784 others injured, according to local health authorities.
The Israeli offensive has left 85% of Gaza's population internally displaced amid acute shortages of food, clean water and medicine, while 60% of the enclave's infrastructure was damaged or destroyed, according to the UN.
In late 2023 South Africa filed a case at the International Court of Justice (ICJ), accusing Israel of failing to uphold its commitments under the 1948 Genocide Convention.
The UN court, in its interim ruling in January, ruled that South Africa's claims are plausible. It ordered provisional measures for Israel's government to desist from genocidal acts, and take measures to guarantee that humanitarian assistance is provided to civilians in Gaza.