The Israeli military said on Wednesday that it had discovered the body of a hostage taken from Israel on Oct. 7, 2023 in an underground tunnel in the area of Rafah in the Gaza Strip, along with evidence that raises questions about the state of another, related captive.

The deceased hostage was identified as Youssef Ziyadne of Rahat, an Arab Bedouin city in southern Israel. Mr. Ziyadne, who was in his 50s, and three of his grown children, were abducted from a kibbutz where he and two of the children had been working during the Hamas-led attack on Israel that ignited the war in Gaza.

Two of Mr. Ziyadne’s children, Bilal and Aisha, both in their late teens, were released during a temporary truce and exchange of hostages for Palestinian prisoners in November 2023.

But the father and his adult son, Hamza Ziyadne, about 22 at the time of his abduction, remained in captivity. The Israeli military noted that the same operation that led to the discovery of Youssef Ziyadne’s body also revealed “findings” related to Hamza, “which raise serious concerns for his life.”

The announcement that a hostage had been found dead, and that the fate of another is uncertain, came as the families of captives and President-elect Donald J. Trump have been pressuring Israel and Hamas to close a deal that would lead to a cease-fire and the return of the remaining captives before Mr. Trump takes office later this month.

Of the 250 hostages taken on Oct. 7, 2023, about 100 remain held in Gaza, with a third or more of those still there presumed dead.