President Joe Biden said Tuesday in an address to the American people, "We stand with Israel. And we will make sure Israel has what it needs to take care of its citizens -- defend itself and respond to this attack."

Biden stressed, "Hamas does not stand for the Palestinian people's right to dignity and self-determination. Their state of purpose is the annihilation of the state of Israel on the murder of Jewish people. They use Palestinian civilians as human shields. Hamas offers nothing but terror and bloodshed, with no regard to who pays the price."

Biden said among the horrors were "parents butchered, using their bodies to try to protect their children. Stomach churning reports of being babies being killed. Entire families slain. ... Women raped, assaulted, paraded as trophies."

"There's still so many families desperately waiting to hear the fate of their loved ones, not knowing if they're alive or dead or hostages," Biden said. "Infants in their mother’s arms, grandparents in wheelchairs, Holocaust survivors abducted and held hostage. Hostages whom Hamas has now threatened to execute in violation of every code of human morality."

"It's abhorrent," Biden said, adding that Hamas' "brutality ... brings to mind the worst rampages of ISIS. This is terrorism. But sadly, for the Jewish people, it's not new."

Biden and Vice President Kamala Harris spoke with Israeli Prime Minister Benjamin Netanyahu earlier in the day.

Biden said, "We're surging additional military assistance, including ammunition and interceptors, to replenish Iron Dome. We're going to make sure that Israel does not run out of these critical assets to defend its cities and its citizens. My administration has consulted closely with Congress throughout this crisis, and when Congress returns, we're going to ask them to take urgent action to fund the national security requirements of our critical partners."

"This is a moment for the United States to come together, to grieve with those who are mourning," Biden said, adding, "There is no place for hate in America -- not against Jews, not against Muslims, not against anybody."

At least 14 Americans have been killed in the Hamas terrorist attacks in Israel, President Joe Biden said Tuesday in an address to the American people.

He condemned Hamas' incursion as an "act of sheer evil."

Biden confirmed that American citizens are among those being held by Hamas.

He said he's directed his "team to share intelligence and deploy additional experts from across the United States government to consult with and advise Israeli counterparts on hostage recovery efforts."

The families of 155 Israeli soldiers have received death notices so far, the Israel Defense Forces said.

The U.S. has started reaching out to the families of Americans missing in Israel as part of its efforts to identify the U.S. citizens who may be among the hostages taken to Gaza by Hamas, according to an official.

But due to the dynamic situation and lack of visibility inside Gaza, the U.S. still can't say how many may be detained.

There's also a level of reluctance from U.S. officials to shine a spotlight on any Americans among the hostages for fear that they might be singled out by their Hamas captors.

Other sources said American officials are working the phones with allies in the Middle East who have leverage over Hamas, encouraging them to pressure the militants to free the hostages.

-ABC News' Shannon Crawford

Six people were killed and dozens were injured when a Gaza school sheltering refugees was hit by Israeli airstrikes, the United Nations Relief and Works Agency said.

At least 4,000 people have taken refuge in the school, UNRWA said.