Israel has not confirmed whether Saturday's strike that killed 90 Palestinians killed two Hamas officials, including military chief Mohammed Deif, Israeli Prime Minister Benjamin Netanyahu said in a press conference.

"There is still no absolute certainty that the two have been eliminated, but I want to assure you that one way or another we will reach the entire top of Hamas," Netanyahu said.

Netanyahu said he was briefed about the type of weapons that would be used and the expected "collateral damage," as well as confirming Israel did not believe any hostages were held in the area, before giving the go ahead for the strike.

"Why should we risk something leaking out? Suppose something leaked, Deif and his deputy would go underground in a second. We update our American friends when necessary," Netanyahu said.

Asked about not telling the U.S. about the strike beforehand, Netanyahu said it was to avoid an information leak.

-ABC News' Anna Burd

The United Nations Human Rights Office has condemned the Israel Defense Forces' use of weapons in populated areas of Gaza, including humanitarian zones, hours after an attack killed 90 Palestinians.

"The latest attack and casualty followed right after another massive attack on the north, which lasted for a week, resulting in further destruction and casualties," the UN Human Rights Office said in a statement.

The U.N. said the IDF's use of weapons in densely populated areas "despite the overwhelming evidence that these means and methods have led to disproportionate harm to civilians and damage to civilian infrastructure, suggests a pattern of willful violation of the disregard of [International Humanitarian Law] principles of distinction, proportionality and precaution."

"The use of such weapons in an area to which IDF is ordering people to evacuate demonstrates a rampant disregard for the safety of civilians. Even if Palestinian armed group members were using the presence of civilians in these areas in an attempt to shield themselves from attack, which would violate IHL, this would not remove IDF's obligations to comply with these fundamental IHL principles of proportionality, distinction and precaution," the U.N. said.

The death toll from Israel's deadly attack on Al Mawasi, west of the southern city of Khan Younis, has now risen to 90 people killed and 300 injured, according to the Gaza Ministry of Health.

Israel had admitted earlier that the strike was in the expanded humanitarian zone.

Israel announced that it was targeting two "senior Hamas terrorists", in a Saturday strike that killed 71 people and injured 289. An Israeli official confirmed to ABC News the two targeted men were Hamas military chief Mohammed Deif and a commander of the Khan Younis brigade Rafa Salama.

It has not yet been confirmed whether they were killed in the strike.

The location struck was an "open area," an Israeli official told ABC News. "The strike was carried out within a fenced area run by Hamas" , in a compound and not a tent camp, the IDF said. But the location was within the humanitarian zone.Witnesses describe multiple strikes, and verified video shows explosions and strikes after first responders arrived on the scene. Victims are visible across a nearby street, and injured women, children and first responders, can be seen in video.

In an official statement, Hamas called the Israeli statements "false claims" and said they were meant as a "cover-up for the scale of the horrific massacre."

"The occupation's fighter jets, artillery, and drones heavily and continuously targeted the tents of the displaced with various types of weapons, resulting in hundreds of martyrs and injured from the unarmed civilians," Hamas said in a statement. "The occupation's claims about targeting leaders are false, this is not the first time the occupation has claimed to target Palestinian leaders, and later it is proven to be a lie."

-ABC News' Samy Zyara, Diaa Ostaz and Dana Savir