Washington — President Biden on Tuesday condemned the Hamas militant group's bloody attacks on Israel that took place over the weekend, calling them an "act of sheer evil" and forcefully declaring that "we stand with Israel."

In remarks delivered from the White House alongside Vice President Kamala Harris and Secretary of State Antony Blinken, the president said the people of Israel experienced "pure, unadulterated evil" at the "bloody hands" of Hamas, which has long been designated a terrorist organization by the U.S.

"This was an act of sheer evil," he said. 

The president revealed that at least 14 Americans are among the more than 900 people killed in Israel, and American citizens are also among those being held captive by Hamas, which controls the Gaza Strip.

National Security Adviser Jake Sullivan said after Mr. Biden's remarks that while he could not confirm the precise number of U.S. citizens who are hostages, there are 20 or more Americans missing. 

"We will work hour-by-hour both to determine whether we can account for any of those Americans, or to confirm exactly the number of Americans held hostage," Sullivan said. "We do not know the number of hostages we have at this time."

Mr. Biden emphasized that "in this moment, we must be crystal clear: We stand with Israel. We stand with Israel."

"And we will make sure Israel has what it needs to take care of its citizens, to defend itself and to respond to this attack," Mr. Biden said. "There's no justification for terrorism. There's no excuse."

Mr. Biden compared the assault on Israel by Hamas to the "worst rampages" of the Islamic State and denounced the "brutality" and "blood-thirstiness" of the group. 

"This is terrorism," he said.

The remarks from the president came after Hamas, the Palestinian militant group that rules the Gaza Strip, launched its surprise assault on Israel early Saturday morning, which the Israel Defense Forces has since said left at least 900 dead and roughly 2,700 wounded. Israeli authorities said dozens of people are being held captive by the group.

The death toll in Hamas-run Gaza is at least 900, according to the Palestinian Health Ministry, though it is expected to rise as Israel continues to launch airstrikes across the Gaza Strip. Another 4,500 are wounded. 

Mr. Biden has repeatedly expressed unwavering support for the Jewish state since the terrorist attack, and reiterated in his latest remarks that the U.S. will "stand united, supporting the people of Israel who are suffering unspeakable losses and opposing the hatred and violence of terrorism."

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

The White House on Monday night was lit in blue and white, the colors of the Israeli flag, as a symbol of "the ironclad support and solidarity of the American people with the people of Israel in the wake of the barbaric terrorist attacks committed by Hamas," according to the White House.

Mr. Biden, along with the leaders of France, Germany, Italy and the United Kingdom, also issued a joint statement condemning Hamas and "its appalling acts of terrorism."

"Our countries will support Israel in its efforts to defend itself and its people against such atrocities," the leaders said Monday. "We further emphasize that this is not a moment for any party hostile to Israel to exploit these attacks to seek advantage."

They added, "All of us recognize the legitimate aspirations of the Palestinian people, and support equal measures of justice and freedom for Israelis and Palestinians alike. But make no mistake: Hamas does not represent those aspirations, and it offers nothing for the Palestinian people other than more terror and bloodshed."

Ahead of his remarks, Mr. Biden met with his national security team to receive an update on the situation in Israel. He and Harris also spoke with Israeli Prime Minister Benjamin Netanyahu to discuss U.S. support for Israel, the White House said.

The U.S. has already moved to provide the Israeli military with additional equipment and resources, including munitions, Defense Secretary Lloyd Austin said Sunday. He also ordered a carrier strike group to move to the Eastern Mediterranean to strengthen regional deterrence efforts. 

The munitions being sent to Israel include small diameter bombs and artillery rounds, according to U.S. officials.

In addition to surging military assistance to Israel, including ammunitions and interceptors to replenish the Iron Dome, Mr. Biden said he has directed his administration to share intelligence with the Israelis and deploy government experts to consult with and advise on hostage recovery.

The president said he will also ask Congress to take "urgent action" to fund the national security requirements of U.S. partners. The House has been in recess since Tuesday following the unprecedented removal of former House Speaker Kevin McCarthy, and the Senate is set to return to Washington next week.

"This is not about party or politics. This is about the security of our world, the security of the United States of America," he said. 

National Security Council spokesman John Kirby told reporters Monday that the first tranche of security assistance is on its way to Israel.

"We fully expect that there'll be additional requests for security systems from Israel as they continue to expand munitions in this fight, and we will stay in lockstep with them, making sure that we're filling their needs as best as best we can and as fast as you can," he said.

Ellee Watson contributed to this report

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