The Israeli military has released footage which it says shows hostages being taken into Gaza's largest hospital after the deadly Hamas attacks of 7 October.
A military spokesman said one of them - a soldier - was killed there.
Cpl Noa Marciano, 19, was killed after being taken into al-Shifa hospital with minor injuries, he said.
Israel has been searching the site it says served as a Hamas command centre. Hamas has denied the claims.
"This morning we updated Noa's family that according to our findings, she was kidnapped to a safe house near Shifa," Rear Adm Daniel Hagari, chief spokesperson for the Israel Defense Forces (IDF), told a news briefing.
"During IDF air strikes in the area, the Hamas terrorist who was holding Noa was killed and she was wounded in the air strike, but not a life-threatening injury. Noa was taken inside Shifa hospital, where she was murdered by another Hamas terrorist."
Hamas has previously claimed Ms Marciano was killed in an Israeli air strike, which the IDF said occurred on 9 November.
Rear Adm Hagari then played CCTV footage which he said was from the morning of 7 October - the day Hamas launched its surprise attack on southern Israel in which 1,200 Israelis were killed and more than 240 taken hostage.
The video showed two hostages being brought into the hospital, Gaza's largest and most modern.
Others were transported in stolen Israeli military vehicles, the spokesman said, pointing to surveillance footage from outside the building.
Back inside, in the corridors of the hospital, armed men can be seen in the CCTV video which is date-stamped 7 October.
One of the hostages appears to be resisting - the other is shown on a stretcher.
The IDF has been under pressure to substantiate its claim that Hamas operated an expansive command centre underneath the vast medical complex in the north of the territory.
Earlier, the IDF released a video that it says shows a tunnel 10m (3ft) below ground that runs for 55m up to a closed - and reinforced - door.
It said this was now part of the evidence that "clearly proves" numerous buildings in the hospital's complex have been "used by Hamas as cover for terrorist infrastructure and activities".
The BBC has not been able to verify the latest evidence put forward.
The US has said it also has intelligence that Hamas has used hospitals in the Gaza Strip, including al-Shifa, as command centres and weapons stores.
John Kirby, a spokesman for the National Security Council said last week that Hamas and another group - Palestinian Islamic Jihad - operate a "command and control node" at al-Shifa.
Israel has cited US intelligence as substantiating their claim of the existence of a major headquarters at the complex but the term "node" may suggest a smaller operation.
Israel believes it is building a credible case and is keen to present evidence as and when it finds it.
The IDF has previously released a computer simulation of what it believes any Hamas base underground at al-Shifa could look like showing a range of different rooms.
The latest video, released by the IDF, appears to show a reinforced tunnel at the hospital but is not yet the evidence that's been promised of the sort of vast and intricate operation depicted in the simulation.
Israel's allies have supported its military campaign of retaliation, which it says is aimed at eliminating Hamas.
But they have expressed a lot of unease at the toll that the offensive - involving air and artillery strikes as well as ground troops - is having on civilians.
The Hamas-run health ministry says the death toll in Gaza since then has reached 12,300. More than 2,000 people are feared to be buried under rubble.
The government of Israeli Prime Minister Benjamin Netanyahu is also under pressure from families of the hostages. They want him to do more to free those held by Hamas.
On Saturday, protesters calling on the Israeli government to prioritise securing the release of hostages walked from Tel Aviv to Jerusalem before holding a demonstration outside Mr Netanyahu's residence.
The prime minister, however, appears undeterred in his mission.
He says his first goal of the war is to destroy Hamas; the second to return the hostages; and the third to eliminate the threat from Gaza.
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