The Israeli military announced on Sunday that, according to an internal investigation, three hostages were probably killed as a result of an airstrike targeting a senior Hamas commander in November.

The investigation’s findings highlight the precarious circumstances of hostages in the Gaza Strip, who — like Palestinian civilians — are vulnerable to Israel’s ongoing military operations in the territory. The findings also suggest that senior Hamas officials, including Yahya Sinwar, the most powerful figure in the group, may surround themselves with hostages as U.S. and Israeli officials have said.

In its statement, the Israeli military said it was “highly likely” that the hostages, Cpl. Nik Beizer, Sgt. Ron Sherman and Elia Toledano, were killed “as a result of a byproduct” of an Israeli military strike targeting Ahmed al-Ghandour, the commander of Hamas’s military wing in northern Gaza.

The military said it was presenting “a high-probability assessment” based on where the hostages’ bodies were found in December, as well as intelligence materials, an analysis of the strike, pathological reports and the conclusions of forensic examiners. Definitively determining the cause of their deaths, the military said, was not possible.

“The I.D.F. shares in the grief of the families over the devastating loss,” the military said.

The three slain hostages, the investigation indicated, were in a tunnel complex used by Mr. al-Ghandour, a top official whose death Hamas later acknowledged. The Israeli military said it had information at the time suggesting that the three hostages were in another place.

The announcement on Sunday came as advocates for the hostages and their families were demanding that Israel’s prime minister, Benjamin Netanyahu, do more to secure a deal with Hamas for the release of the dozens of living hostages still in Gaza, even if that allows Hamas to survive the war with Israel.