By Chloe KimBBC News

At least 22 American citizens are confirmed to have died after Hamas launched its deadly attack on Israel, the US state department has said.

At least another 17 Americans are missing, the White House confirmed.

It is unclear how many of those may been taken captive by the Palestinian militant group.

The death toll from the attack in Israel has reached 1,200. More than 1,100 people have died in Israeli air strikes on Gaza.

US Secretary of State Antony Blinken confirmed the updated figure on Wednesday, posting on X: "We join families in Israel, in the US, and around the world mourning the loss of loved ones killed in Hamas's heinous attacks.

"We continue efforts to secure the release of those hostages, and the US remains steadfast and unwavering in our support for Israel," he wrote.

White House spokesman John Kirby warned the numbers could rise: "I think we all need to steel ourselves for the very distinct possibility that these numbers will keep increasing, and that we may in fact, find out that more Americans are part of the hostage pool," he said.

Speaking at a roundtable discussion with Jewish leaders on Thursday, President Biden accused Hamas of mounting a "campaign of pure cruelty" and said it was among the darkest days for the Jewish community since the Holocaust.

Regarding the ongoing hostage situation, he told the audience that if he shared all the details of efforts to free Americans he "wouldn't be able to get them home".

More on Israel-Gaza attacks

A number of Palestinian-Americans are also reported to be stuck in Gaza, though it is unclear if any of them have been injured in the bombardment.

The US Embassy in Jerusalem said in a security alert on Monday: "US citizens in Gaza who wish to leave and can do so safely are advised to check the status of the Rafah Crossing into Egypt."

The state department increased its travel alert warning level on Wednesday, advising Americans to reconsider any plans to visit Israel and the West Bank.

Among the missing Americans is 23-year-old American-Israeli Hersh Golberg-Polin, who was at a music festival in the desert when it was stormed by militants.

His parents told the Jerusalem Post they received two messages from him, reading "I love you" and "I'm sorry".

"We just want him safe," Jonathan Polin, his father, said.

Another US citizen living in Israel, Abbey Onn, told the BBC's partner CBS that five members of her family, including a 12-year-old boy, were taken hostage.

On Saturday, she received a WhatsApp message from her family that Hamas fighters were in their home at Nir Oz, a kibbutz near Gaza.

Judith and Natalie Raanan, a mother and teenage daughter from Chicago, Illinois, were visiting relatives in southern Israel when the attack began.

Judith's ex-husband, Natalie's father, told a local news station the pair had texted him that they were hiding in a safe room, but he had not heard from them since.

A soldier with dual US-Israeli citizenship, Itay Chen, has been reported missing in action since Saturday.

His father, Ruby Chen, told CBS he had sought the state department's help in finding his son, who he said had grown up in New York City.

He added that it is "a fair assumption" his son was taken to Gaza.

Mr Kirby said the US wants to get all hostages back with families, particularly the American ones, but the US does not know where the hostages are, whether they are all together or how often they are being moved.

US National Security Adviser Jake Sullivan said the US was in regular contact with the families of the missing.

The identities of all the Americans killed have not yet been officially released, but some family members have been announcing the news online or speaking to local media.

Ilan Troen, a professor at Brandeis University in Massachusetts, said his daughter Deborah Matias, 50, and her husband, Shlomi, were killed when Hamas fighters attacked their community in southern Israel.

Mr Troen said his daughter died while shielding their son, Roten.

"They made sure to fall on him and thereby saved his life," he told CBS. "Although a bullet actually entered his abdomen, but he was saved."

Long-time Israel resident Hannah Katsman, a native of Cincinnati, Ohio, wrote on Facebook that her son Hayim Katsman was killed at his kibbutz near the border with Gaza.

Mr Katsman, an academic who specialised in Israel studies, graduated from the University of Washington.

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