The four men were identified as Chaim Peri, 80, Yoram Metzger, 80, Amiram Cooper, 84, and Nadav Popplewell, 51.
All four were filmed alive in hostage videos posted by Hamas. Hamas said that Popplewell had died of wounds sustained during an Israeli air strike when posting his video last month.
Military spokesperson Rear Admiral Daniel Hagari said that new intelligence led to confirmation of their deaths.
The military believes the four were killed together in the southern Gaza city of Khan Younis a "number of months" ago when Israeli forces were operating in the city, Hagari said in remarks that were broadcast.
"We are thoroughly examining the circumstances of their deaths and checking all possibilities. We will present soon the findings, first to their families, and then to the public," he said. "We will present them with transparency, as we have done until now."
Of the more than 250 people abducted on October 7, about 120 remain in Gaza, according to Israeli tallies. Many have been declared dead by Israeli authorities.
Peri was at his house in Kibbutz Nir Oz during the Hamas attack. He tried to repel the gunmen while hiding his wife behind a sofa, his son later told Reuters. He eventually gave himself up to save his wife, who remained hidden, his son said.
Cooper and Metzger, also from Nir Oz, were captured along with their wives, both of whom were returned to Israel during a brief November truce.
Popplewell, according to a hostages support group, was captured with his mother from her home in Kibbutz Nirim. His brother was killed during the attack. His mother was freed during the November truce.
