JERUSALEM (AP) — The Hamas -run Gaza Strip is a tiny enclave, measuring 40 kilometers (25 miles) long and no more than 12 kilometers (7 miles) wide, surveilled continually by Israel, surrounded by its guns. But rescuing — or even locating — more than 150 hostages hustled there by Palestinian militants who overran Israel’s southern border on Saturday will be a daunting task.

Gaza’s densely populated terrain, its network of underground tunnels and the sheer numbers of men, women and children taken captive present Israel with the most complex hostage crisis that the country has ever faced.

Mounting rescue operations in the midst of the massive Israeli bombardment of Gaza that followed the deadly Hamas rampage in southern Israel would only make an already difficult mission even more formidable.

“The situation is unprecedented,” said Gershon Baskin, who helped to negotiate the 2011 release of Staff Sgt. Gilad Schalit after more than five years of Hamas captivity. “I think Hamas was surprised at the ease it was able to take hostages. Israel was completely bewildered by everything that’s happened.”

Images of hostages have become seared into Israel’s collective consciousness. The panicked woman being dragged off by militants on a motorcycle, her boyfriend marched across the border on foot. The terrified mother, wrapped in a blanket, clasping her two young children.

Eli Elbag had tried for 12 hours to contact his soldier daughter Liri, 18, who was training to be a lookout at the Gaza border. Then a friend sent a video showing her crowded into the back seat of an Israeli military truck that militants had commandeered, sitting next to two other hostages, one with blood covering his face.

As Israel pummels neighborhood after neighborhood in Gaza, Elbag and his wife have been glued to the television, looking for any sign of her. He said he understands the Israeli operation but remains concerned for Liri’s safety.

“Nobody,” said Elbag, “can understand what we are feeling.”

Hamas has demanded freedom for all 5,200 prisoners the Palestinians say are held in Israeli jails in exchange for the captives. It has warned it will kill a hostage every time Israel’s military bombs civilian targets in Gaza without warning.

The group is also holding the bodies of two Israeli soldiers killed in the 2014 war between Israel and Hamas, as well as two Israeli civilians who entered its territory years ago.

Information about the hostages seized Saturday remains sketchy days later. No complete list has been released, and it’s not clear who is alive and who is not. Many are Israelis, but a long list of other countries have said their citizens have been taken hostage.

Hamas has traditionally treated hostages as valuable assets, revealing little to no information about their conditions or whereabouts and refusing to grant the International Committee of the Red Cross access to check on their well-being.

On Tuesday, United States President Joe Biden confirmed that Americans were among the captives. The United States has offered to share its expertise in hostage recovery with Israel, said John Kirby, the spokesperson for the National security Council at the White House.

“Nothing is more important to President Biden than make sure we look after the safety and security of Americans overseas,” Kirby told Israel’s Channel 12 TV in an interview. “And we will continue to work with the Israelis on this hostage recovery crisis, and do whatever we can do, do whatever is appropriate to do, to help them as they work their way through those kinds of decisions.”

Some hostages are dual nationals, and that will further complicate Israel’s efforts to free them, Bruce Hoffman, a senior fellow at the Council on Foreign Relations, wrote in a briefing. He said the captives have likely already been dispersed throughout Gaza, and their hiding places and perhaps even the hostages themselves are likely to be laden with traps.

“This is a challenge of a magnitude that has never been faced before,” Hoffman wrote. “How this crisis will end is anyone’s guess, but the shedding of more innocent blood — Israeli, Palestinians, and indeed non-combatant citizens of other countries — is certain.”

The unique nature of the crisis does contain advantages for Israel, Baskin said. Because there are so many captives, information about some of their locations might leak, even though they are likely dispersed around the territory in homes or underground, he said. That could favor rescue operations.

Israel has historically made big concessions to win freedom for hostages, almost all of them over soldiers or their remains. Its history of lopsided prisoner exchanges included the trading of Schalit for more than 1,000 Palestinian prisoners, including the current Hamas leader in Gaza, Yehia Sinwar.

The fate of prisoners is emotionally charged on the Palestinian side, too; most Palestinians have either spent time in an Israeli jail or know someone who did.

But as Israel’s military strikes Gaza with unprecedented ferocity, it’s not clear whether the safety of hostages is playing a role in decision-making. At least one member of the government, the hard-line Finance Minister Bezalel Smotrich, who also plays a role in the Defense Ministry, was quoted as demanding Saturday that the military “hit Hamas brutally and not take the matter of the captives into significant consideration.”

Reports of Egyptian, Turkish and Qatari mediation efforts don’t appear to be going anywhere. More than 1,200 Israelis were killed in Hamas’s incursion, so Baskin doesn’t expect Israel to engage in a negotiated deal that would reward the militant group.

In Israel, he said, “no one has the appetite to give Hamas any kind of prize.”