In a subterranean compound deep below Khan Younis, a Hamas stronghold in the southern Gaza Strip, the five cells with barred doors that the Israeli military says held hostages abducted from Israel had clearly been constructed long in advance.

The tunnel builders even paid some attention to décor: The tiled walls of a small kitchenette in the compound, littered with remnants of food and dirty dishes, were embellished with a quaint, if incongruous, motif of teapots and teacups.

The Israeli military said that roughly 20 hostages were kept in the compound at various times. It said it pieced that assessment together based on testimony it said it gathered from the captives, as well as evidence like DNA. Some were released among the more than 100 hostages freed during a weeklong truce in late November, while others, including older people, were later dispersed to other locations in Gaza, the military said.

There has been no independent confirmation of the Israeli account of the compound, but details provided to Israeli media by one of the hostages — who was freed in November and, Israel says, held in the Khan Younis compound — aligns with some of those assertions.

Some 240 captives were seized during the Hamas-led Oct. 7 attack on southern Israel, in which about 1,200 people were killed, according to Israeli officials. More than 25,000 Gazans have been killed so far, most of them civilians, according to health authorities in the enclave, following a punishing counterattack by Israel.

A journalist for The New York Times descended on Friday morning into the dark labyrinth leading to the compound under Khan Younis, escorted by Israeli soldiers and military officials to show what they said were the conditions in which the hostages had been held.

An arched chamber at the mouth of the corridor leading to the cells with barred doors was covered with green carpeting, like fake grass, and strewed with detritus.

Amid a jumble of blankets with floral patterns and plastic bottles lay several empty tubes labeled RPG-7VR, a kind of rocket-propelled grenade, and bearing the insignia of Hamas’s military wing, the Qassam Brigades. In a dim corner, there were four standing fans, a half-used pack of disposable diapers and a metal Palestine Red Crescent Society first-aid case containing a packet of latex gloves and a few sealed gauze pads.

The guided visit to the compound came as Israel, after more than 100 days of fighting in Gaza, appeared increasingly torn between the dueling war goals of dismantling Hamas’s military and its governing abilities and of freeing the remaining 130 or so captives, which will most likely require a diplomatic deal involving a cease-fire.

At least 25 of the captives have already been declared dead, and many Israelis fear that time is running out for the rest. The military offensive has slowed, complicated by the sheer scope and sophistication of Hamas’s vast tunnel network that crisscrosses the Palestinian enclave, extending for hundreds of miles, according to Israeli intelligence.

Beneath Khan Younis alone, the military estimates that Hamas dug at least 100 miles of tunnels across several levels, creating an inverted, multistory complex.

“We are fighting in Khan Younis above ground and below ground,” said Rear Adm. Daniel Hagari, the chief spokesman for the Israeli military, who led the tour of the subterranean compound on Friday. He added, “This kind of warfare is unlike any other modern battlefield anywhere in the world.”

The spiraling death toll in Gaza has increased international pressure on Israel to end the war. Above ground, much of Gaza is in ruins.

“Israel does not seek destruction,” Admiral Hagari said. “This war is a tragedy.” But there is no way to destroy tunnels built beneath civilian areas without damaging the structures above, he said, adding, “Hamas knows that.”

The Times and other journalists accepted a military escort to visit the underground compound and secure rare access to wartime Gaza, which is mainly off-limits to the outside news media.

After a half-hour journey in an armored vehicle, the journalists were taken to a ground-level entrance with an open metal door in the side of a three-story apartment building that led down a staircase to a maze of tunnels that branched out in different directions. The neighborhood, in eastern Khan Younis, had been evacuated.

The tunnel entrance, located under the residence of a Hamas operative, was booby-trapped with explosives, according to the Israeli military. As soldiers of the 98th Paratroopers Division advanced along the underground route, they encountered blast doors and engaged in close combat with several fighters, who were killed, the military said. By the time the soldiers reached the carpeted chamber and cells, the hostages had been moved to another location, the military said, without saying when it believed hostages had last been present there.

The compound was about a half-mile into the warren of tunnels, which was lined with electricity and communications cables, and about 65 feet — or about six floors — underground. To reach it required walking single file through pitch darkness and walking down long flights of stairs carved into the earth. The air was thick and humid.

In the abandoned chamber, which was equipped with basic light fittings, the Israeli military said soldiers had found two drawings by a child. The military showed photographs of the drawings — both of a house against a backdrop of hills with a sun and clouds in the sky — that it said were drawn by Emilia Aloni, 5, an Israeli girl who was abducted with her mother, Danielle Aloni, 44, on Oct. 7 from Kibbutz Nir Oz. After nearly seven weeks in captivity, the Alonis were released in a first group of 13 hostages, all women and children, under the temporary truce deal in November.

In interviews with Israeli television channels after the hostages’ release, Ms. Aloni displayed pictures she said were drawn by her daughter in captivity that closely resembled those the Israeli military said had been found in the compound under Khan Younis.

In the television interviews, Ms. Aloni said she and her daughter were taken into a tunnel soon after arriving in Gaza and then walked for hours in what she described as an “underground city.” Eventually, she said, they came to a kind of “cave” where there were about a dozen other captives, including wounded older people and a teenager.

Ms. Aloni recalled sleeping on mattresses next to other hostages in extremely humid conditions with little air, making it hard to breathe.

The Alonis were held underground for several days and then moved to an apartment above ground where they stayed for nearly two weeks with other hostages, Ms. Aloni said. They were then returned to the tunnels for safety, she said, as Israeli fighter jets pounded Gaza.

Ms. Aloni appeared in a hostage video in late October with two other women, Rimon Kirsht, 36, and Yelena Trupanob, 50, who were also released a month later.

In a document released on Sunday by Hamas in which it provided its own narrative of recent events, the group said that it “dealt in a positive and kind manner with all the civilians who have been held in Gaza.”

Many of the released hostages say they received little food and water, inadequate medical treatment, if any, and were kept in tough conditions.

The Israeli military said some of the hostages were kept in the central chamber and others in the narrow cells with the barred doors. The cells had clinical white-tiled walls broken by a vertical purple stripe with a toilet and sink in the back of each one; some also had a small shower nozzle. Soldiers escorting the journalists said that strands of hair had been found in the cells, as well as a bra. The military said DNA testing matched the hair with hostages, but did not say who.

Ayala Metzger, the daughter-in-law of Yoram Metzger, 80, who is still a captive in Gaza, told Israel’s Channel 12 News on Sunday that his DNA was found on clothes left behind in the compound.

A boiler provided hot water when there was electricity.

Any hostages kept in the compound would have had little sense of time below ground, or of the destruction taking place on the surface.

Emerging back into sunlight two hours after entering the tunnel, the subterranean silence was replaced for the reporters accompanying the Israeli military on Friday by the sounds of war. A drone whined in the sky. Sharp cracks and booms stirred up plumes of dark smoke.

The neighborhood is a wasteland, surrounded by mounds of earth and rubble and churned up roads.

Inside the house that Israel says belonged to the Hamas operative, a marble staircase hinted at a level of opulence. Copper and gold curtains still hung at blown-out windows in a lower-floor bedroom, and most of an outside wall had gone. Not one building in the vicinity looked habitable.

By Saturday, the tunnels and the compound below the neighborhood had been blown up.

Myra Noveck contributed reporting from Jerusalem.