At least 22 U.S. citizens have been killed during the Hamas attacks on Israel, National Security Council spokesperson John Kirby said at a news conference Wednesday. 

Kirby couldn't confirm details on where or how the Americans were killed, as the "individual circumstances are not exactly clear," he said. 

The attacks have claimed more than 1,200 lives in Israel. At least 1,100 have been killed in the Gaza Strip, the Gaza Ministry of Health said Wednesday. 

Seventeen Americans remain unaccounted for, Kirby said on Wednesday. "A number" of the missing are hostages of Hamas, he said, but would not give a number. 

"We need to steel ourselves for the very distinct possibility these numbers will keep increasing," said Kirby.  He said,"more Americans might be part of the hostage pool." 

Addressing the families of the missing and killed Americans Kirby said, "We are grieving with you. We're sorrowful with you. We're worrying with you and we're going to do everything we can." 

Kirby said that the U.S. offered assistance and counsel to Israel for hostage recovery. 

Officials have not released information on the individuals killed, but Kirby said the U.S. State Department is actively working to reach out to the involved families. 

Some family members have confirmed to CBS News the deaths of their loved ones. Academic and professor Hayim Katsman was murdered on Oct. 7 at Kibbutz Be'eri in Southern Israel while helping his neighbor and her children, his uncle told CBS Seattle affiliate KIRO. 

Abe Katsman said his nephew was trying to hide the mother and her children when Hamas terrorists burst in and shot him. Katsman said his nephew was a "skilled auto mechanic, a more than adequate musician, and a horticulturist." 

While studying the interrelations of religion and politics in the Middle East at the University of Washington, Katsman won the Baruch Kimmerling Prize in 2020 for best graduate paper, according to his university profile.

Deborah Matias, 50, and her husband Shlomi, were killed by members of Hamas militant groups during Saturday's attack, her father, professor Ilan Troen, told CBS News Boston. Troen said his daughter's last act of motherhood was defending her son, 16-year-old Roten, who is in a hospital recovering from his injuries.

"[Deborah and Shlomi] loved music, life, each other, their kids. I would ask him to think of the joy that they sought and had in their lives rather than the focus on that day," Troen said.

The parents of Aryeh Ziering, a 27-year-old Israeli-American, told CBS News on Saturday their son — who had remained in the Israeli military after his mandatory service because he wanted to protect his country — was one the first soldiers killed in action in southern Israel during Hamas's violent attacks on Saturday, his parents said.

Soldiers knocked on the Ziering's door on Sunday morning — "a knock you never want to get," his parents Debbie and Mark said, to inform them their son had died.

His father said Ziering is still very present and he can feel his energy, "but he's not coming back."

In:
• Hamas
• Israel

Cara Tabachnick

Cara Tabachnick is a news editor for CBSNews.com. Contact her at [email protected]