As the humanitarian crisis worsens in Gaza, Israeli Energy Minister Israel Katz said no electrical switch will be turned on, no water tap will be opened and no fuel truck will enter Gaza until the Israeli hostages are returned home.

Gaza relies on Israel for most of its power, which was cut off following the attack. Its sole power plant ran out of fuel on Wednesday.

The White House said there are no intentions to send U.S. troops to Israel.

"The Israelis have made it very clear that they don't want foreign troops on their soil. That they want to prosecute these operations on their own and they have every right to want to do that," said John Kirby, spokesperson for the National Security Council.

Kirby said the U.S. would "do everything we can to improve" the capabilities of the Israeli military.

And as humanitarian concerns grow in Gaza, Kirby told reporters that there are "ongoing conversations" with Israeli counterparts about the need for the "continued flow of humanitarian assistance" to the area.

-ABC News' Justin Gomez and Molly Nagle

The death toll of American citizens in Israel now stands at 27, John Kirby, spokesperson for the National Security Council, said at a White House briefing on Thursday.

Fourteen Americans remain unaccounted for.

At a news conference Thursday, Secretary of State Antony Blinken was asked about the gruesome photos and videos shown to him behind closed doors by Israeli Prime Minister Benjamin Netanyahu.

"It’s beyond what anyone would ever want to imagine, much less, God forbid, experience. A baby, an infant -- riddled with bullets. Soldiers beheaded. Young people, burned alive," he said. "I could go on, but it’s simply depravity in the worst imaginable way."

Blinken said that some of the images had been seen before, but others were new to him, and again said that Hamas’ acts harkened back to ISIS.

"I think for any human being to see this -- it’s really beyond almost anything that we can comprehend, digest," Blinken continued. "You can’t help but imagine yourself, your family, your loved ones, your friends in that situation, in that predicament and maybe the best word for it for me is overwhelming."

While some of the claims made by the IDF have been questioned and others have fueled online claims that the Israeli government is spreading disinformation, Blinken said that the photos would ultimately show exactly the horrors its people have confronted and serve to unify through "moral clarity."

-ABC News' Shannon Crawford

Human Rights Watch has accused Israel of using white phosphorus munitions in military operations in Gaza on Wednesday, saying it violated international humanitarian law by putting civilians at unnecessary risk.

In a report released Thursday, Human Rights Watch said it based its determination on a video it said it has verified, as well as two eyewitness accounts.

The Israel Defense Forces said in a statement to ABC News that claims they used white phosphorus in Gaza are "unequivocally false."

ABC News geolocated a video showing a jellyfish-shaped plume of white smoke over the port of Gaza. The video was posted on Wednesday by the official Palestinian news agency WAFA and matches images posted on social media and by other news outlets on the day.

Two experts -- Amael Kotlarski, the weapons team manager for the defense intelligence firm Janes, and Amnesty International weapons investigator Brian Castner -- told ABC News that images suggested munitions deployed over the port of Gaza on Wednesday appeared to contain white phosphorus.

"We have verified that Israeli artillery forces striking Gaza are equipped with M825 and M825A1155mm white phosphorus projectiles," Castner told ABC News, pointing to photographs by an Anadolu Agency photographer taken on Monday and showing Israeli troops handling shells labeled "M825A1."

Kotlarski said visual evidence alone was not sufficient to confirm that these specific shells were used in the Gaza port strikes.

There are "perfectly legal" military uses for white phosphorus munitions, Kotlarski said, including to create a smoke screen to conceal movements, to mark targets for artillery or air strikes, or to illuminate a battlefield. However, its use in urban areas is "problematic due to the higher risk of collateral damage," Kotlarski said, including the munitions' potential to cause severe burns.

White House Principal Deputy Press Secretary Olivia Dalton said Friday the U.S. had not independently verified allegations Israel used white phosphorous "so that is not something I would want to speculate about or weigh in on at this time."

-ABC News' Christopher Looft, Ben Gittleson and Jordana Miller