WASHINGTON — President Joe Biden on Tuesday confirmed that U.S. citizens are among the hostages captured by Hamas as he condemned the militant group for the “sheer evil” of its shocking weekend assault on Israel.

“Our hearts may be broken but our resolve is clear,” said Biden, who compared the brutality of the Hamas militants to that of the Islamic State terrorist group. He added: “Let there be no doubt. The United States has Israel's back. We'll make sure the Jewish and democratic state of Israel can defend itself today, tomorrow as we always have.”

The president coupled his unflinching defense for Israel with only a glancing reference to the suffering that innocent Palestinians are enduring from Israel's barrage of retaliatory fire on the Gaza Strip, where the Hamas attack was launched. That hardline approach could prove more difficult to sustain going forward if, as expected, the humanitarian crisis for the Palestinians worsens as Israel expands its military operation to root out Hamas.

Biden took note of the impact on Americans as well. He said the number of U.S. citizens confirmed to have been killed in the fighting has reached 14, up from 11 reported previously. U.S. officials said that death toll could increase further as some 20 Americans remain unaccounted for.

“There's no justification for terrorism. There's no excuse,” Biden said. “Hamas does not stand for the Palestinian people's right to dignity and self-determination. Their stated purpose is the annihilation of the state of Israel and the murder of Jewish people. They use Palestinian civilians as human shields.”

Hamas responded to Biden's remarks with a statement defending its actions, saying they were fighting against an occupation and defending Palestinians' right to self-determination. Hamas called on Biden to “move away from the policy of double standards” when it comes to Israel.

Biden and Vice President Kamala Harris spoke by phone earlier Tuesday with Israeli Prime Minister Benjamin Netanyahu to discuss the unfolding situation. Biden outlined the actions he and other allies have taken to support Israel in the aftermath of the attack and expressed his horror about “sickening” reports of torture inflicted by militants on civilians.

Biden, in his public remarks and statements since Hamas launched its attacks, has repeatedly emphasized his shock over the breadth and brutality of the Hamas assault — a blitz by land, sea and air that surprised Israeli and U.S. intelligence and that has killed hundreds Israelis and left even more wounded.

Sen. John Fetterman, D-Pa commented on the attacks Monday.

“I unequivocally support any necessary military, intelligence, and humanitarian aid to Israel. The United States has a moral obligation to be in lockstep with our ally as they confront this threat,” Fetterman said. “I also fully support Israel neutralizing the terrorists responsible for this barbarism.”

Retaliatory strikes by Israel on the Gaza Strip have also left hundreds of dead and wounded Palestinians in the blockaded 141-square-mile area, one the poorest places in the world. The death toll was expected to grow as Israel pummeled Gaza with airstrikes and sent tens of thousands of Palestinians fleeing into U.N. shelters.

Biden said he has directed his team to share intelligence and military experts to consult and advise Israelis.

He renewed his warnings to adversaries who might want to exploit the turmoil. “Let me say again to any country, any organization, anyone thinking of taking advantage of the situation,” Biden said. “I have one word: Don't.”

White House national security adviser Jake Sullivan said the U.S. does not know the precise number of Americans taken hostage. He said that the U.S., at the moment, has no plans of putting U.S. troops on the ground.

“As president I have no higher priority than the safety of Americans being held hostage around the world,” Biden said.

Biden is also dispatching his top diplomat to Israel to show U.S. support after the attacks, the State Department said Tuesday.

State Department spokesman Matthew Miller said Secretary of State Antony Blinken would travel in the coming days to deliver a message of solidarity and support. He said Blinken will also “talk about what additional resources we can give them.”

Blinken will leave Wednesday and is expected to arrive Thursday.

The White House on Monday confirmed that it has already begun delivering critically needed munitions and military equipment to Israel, and the Pentagon was reviewing its inventories to see what else can be sent quickly to boost its ally in the war against Hamas.

The Ford carrier strike group has arrived in the far Eastern Mediterranean, within range to provide a host of air support or long-range strike options for Israel if requested, but also to surge U.S. military presence there to prevent the war from spilling over into a more dangerous regional conflict, officials said.

The Pentagon has said that the U.S. warplanes, destroyers and cruisers that sailed with the Ford will conduct maritime and air operations which could include intelligence collection, interdictions and long-range strikes.

Along with the Ford, the U.S. is sending the cruiser USS Normandy and destroyers USS Thomas Hudner, USS Ramage, USS Carney and USS Roosevelt, and the U.S. is augmenting Air Force F-35, F-15, F-16, and A-10 fighter aircraft squadrons in the region.

Sullivan said the U.S. has already replenishing munitions for Israel's Iron Dome missile defense system from U.S. stock that was already staged in country. The U.S. was in the process of sending additional interceptors and the administration was looking at additional ways it can help augment Israel air defense capabilities, Sullivan said.

Defense Secretary Lloyd Austin told reporters traveling with him Tuesday to a Ukraine contact group meeting in Brussels that a small group of U.S. special operations forces is also working with the Israelis to help with planning and intelligence.

Americans have had a gloomy outlook on Biden's performance on the Israeli-Palestinian issue. Six in 10 Americans (61%) disapproved of how Biden was handling the conflict between the Israelis and Palestinians, according to an August poll from The Associated Press-NORC Center for Public Affairs Research. About one-third (35%) of U.S. adults approved, which was slightly lower than Biden's overall approval rating of 42% in the same poll.

Four in 10 Americans (44%) said the U.S. gives about the right amount of support to Israel in the conflict between the Israelis and the Palestinians. Republicans were more likely than Democrats to say the U.S. should offer more support to Israel. Four in 10 Americans (42%) said the correct amount of support is given to the Palestinians. Democrats and Independents were more likely than Republicans to say the Palestinians should receive more support.

The current crisis seems certain to further test public sentiment about Biden's Mideast foreign policy approach.

The Biden White House has pointed to its handling of the last conflict between Israel and Gaza in 2021 as playing a crucial part in limiting the length and loss of life in a war that stretched over 11 days and killed at least 250 people in Gaza and 13 in Israel.

During the 2021 conflict, Biden limited his public commentary while pressing Netanyahu in private to end it. His behind-the-scenes effort played out even as some of the president's fellow Democrats pressured him to speak out against the Israelis as the death toll climbed in Gaza and as tens of thousands of Palestinians were displaced by the aerial bombardment, White House officials said at the time.

But this conflict is unlikely to end so quickly. Domestic and international pressure could quickly mount on Biden to pressure Netanyahu to wind down operations to prevent the suffering of innocent Gazans.

Netanyahu said Saturday that civilians in Gaza should leave areas near where Hamas is operating as the Israeli military planned to take defining action against the militant group.

Sullivan said U.S. government officials have discussed details with Israel and Egyptian officials about where people in Gaza should go.

But Biden seemed to make clear that he's not asking Netanyahu to show restraint.

“Like every nation in the world, Israel has the right to respond, indeed has a duty to respond to these vicious attacks.” Biden said.

Rep. Mike Kelly, R-16th, echoed these sentiments in a statement Tuesday as he joined a bipartisan resolution standing with Israel.

“Let's be clear: the United States must stand with Israel,” Kelly said. “Our strongest ally in the Middle East is under attack by Hamas terrorists. I condemn these senseless and unprecedented attacks. I support Israel's right to protect and defend itself and its people in this war.”

Bishop David Zubick, of the Catholic Diocese of Pittsburgh, issued a statement Sunday on the weekend of violence. Zubick said news of attacks targeting civilians in Israel parallel the violence wrought by the Tree of Life shooting in Squirrel Hill five years ago.

“Joining my voice to the prayers of all believers in this region of Southwestern Pennsylvania, I implore all leaders involved to seek ways to diminish the conflict and to pursue justice and peace for Israelis and Palestinians alike,” Zubick said.

On Tuesday, Gov. Josh Shapiro wrote on the social media platform X, formerly known as Twitter, that he had ordered U.S. and commonwealth flags to fly at half-staff across the state through Friday to honor lives lost in Israel.

“Pennsylvania stands in solidarity against terror and is praying for all people in Israel,” he said.