(NewsNation) — After days of relentless fighting in Israel, the United States confirmed at least 11 Americans are among the dead.

In a statement, President Joe Biden expressed sympathy for the families of Americans who were killed in the violence as well as those missing and potentially being held as hostages.

“As we continue to account for the horrors of the appalling terrorist assault against Israel this weekend and the hundreds of innocent civilians who were murdered, we are seeing the immense scale and reach of this tragedy,” Biden said in a statement. “Sadly, we now know that at least 11 American citizens were among those killed—many of whom made a second home in Israel.”

State Department Spokesperson Matthew Miller also told NewsNation there are U.S. citizens missing, but did not say how many. The administration is working to locate the missing Americans, who the government believes could be held hostage by militant group Hamas.

“We extend our deepest condolences to the victims and to the families of all those affected,” Miller told NewsNation. “We continue to monitor the situation closely and remain in touch with our Israeli partners and the local authorities. We are in touch with the families and providing all appropriate consular assistance.”

Biden also expressed support for Americans who may be stuck in Israel as major airlines have suspended flights to and from Tel Aviv, saying the State Department was providing assistance and security updates to American citizens.

“I have directed my team to work with their Israeli counterparts on every aspect of the hostage crisis, including sharing intelligence and deploying experts from across the United States government to consult with and advise Israeli counterparts on hostage recovery efforts,” he added.

In his statement, Biden referred to the U.S. and Israel as “inseparable partners,” condemning the attack by Hamas and pledging unwavering support to the country.

“In this moment of heartbreak, the American people stand shoulder-to-shoulder with Israelis. We remember the pain of being attacked by terrorists at home, and Americans across the country stand united against these evil acts that have once more claimed innocent American lives. It is an outrage,” he said.

In the meantime, the White House said security assistance will be sent to Israel, with Biden speaking to Israeli Prime Minister Benjamin Netanyahu in a call after the country declared war on Hamas.

The violence began when Hamas launched a surprise attack during a major Jewish holiday, attacking communities near the Gaza Strip. During the fighting, gunmen killed civilians as well as soldiers and took hostages from the area.

In retaliation, Israel launched airstrikes and vowed to lay siege to Gaza, though it is not yet known if the war will include a ground assault.

Already, hundreds have been killed on both sides, many of them civilians, and thousands more injured in the fighting.

The U.S. is moving a carrier strike group to the Eastern Mediterranean and sending fighter jets over as a warning to Iran after a spokesperson for Hamas said the country provided support for the attack. The U.S. has not confirmed direct Iranian involvement but said Iran’s support of Hamas makes it broadly complicit.

Biden has promised to support Israel in the conflict.

“The United States stands with the people of Israel in the face of these terrorist assaults. Israel has the right to defend itself and its people. Full stop. And my administration’s support for Israel’s security is rock solid and unwavering,” Biden said.

No White House briefing is scheduled for Monday, even as reporters have many questions about how U.S. and Israeli intelligence missed signs of the attack.

National Security Council spokesman John Kirby told NewsNation on Monday that Hamas taking hostages was another example of their “barbarity” and he is “publicly calling for Hamas to release every single hostage in their possession.”

The death toll ups the stakes for the Biden administration as the president told his top advisers to work with regional partners to “warn anyone who might seek to take advantage” of the escalating violence in the Middle East.

During a Monday morning meeting, President Biden met with Secretary of State Antony Blinken, National Security Adviser Jake Sullivan and other aids to discuss the situation in Israel. The White House said in a statement that the president “directed his team to follow up on coordination with Israel on all aspects of the crisis.”

In a joint statement release on Monday, the top leaders of France, Germancy, United Kingdom, and Italy with the United States condemned the attack.

“Today, we — President Macron of France, Chancellor Scholz of Germany, Prime Minister Meloni of Italy, Prime Minister Sunak of the United Kingdom, and President Biden of the United States — express our steadfast and united support to the State of Israel, and our unequivocal condemnation of Hamas and its appalling acts of terrorism,” the statement read.

They emphasized that there is no justification for terrorism and cited recent heinous actions by Hamas, including attacks on families, a music festival, and the kidnapping of civilians. 

The leaders pledged their collective support to assist Israel in defending itself and cautioned against any attempts by parties hostile to Israel to exploit the situation. While acknowledging the legitimate aspirations of the Palestinian people, they stated that Hamas does not represent those aspirations and only brings more violence. 

“Over the coming days, we will remain united and coordinated, together as allies, and as common friends of Israel, to ensure Israel is able to defend itself, and to ultimately set the conditions for a peaceful and integrated Middle East region,” the statement concluded.