Hamas Took Scores of Hostages From Israel. Here’s What We Know About Them.

Hamas, the group that controls Gaza and staged the brazen surprise attack on Israel, has taken scores of hostages since storming across the border in a deadly assault that began Saturday.

Here’s what we know about the captives.

How many hostages are there?

The Israeli authorities have not yet publicly provided specific details about the number or identities of the kidnapped victims, but military officials have said they included older people and children. Most were captured from small Israeli border towns on Saturday morning.

At least 150 Israelis were taken hostage by Palestinian assailants, according to a preliminary assessment shared by one senior Israeli military official. Officials from the United States, France and several other countries have said they were looking into reports that their citizens may be among the captives.

Who are they?

Most information about those who may have been taken hostage has come from people searching for their missing relatives and friends.

Some appear to have been taken from their homes in the Israeli border communities that were overrun by Palestinian gunmen on Saturday. Others appear to have been seized from a wooded area near the border where they had spent the night at a festival.

Distraught and fearful, their relatives have turned to news organizations and social media platforms, sharing photographs of those who are missing and sharing videos online to solicit clues.

Where are they being held?

Abu Obeida, a spokesman for Hamas’s armed wing, claimed in a statement on the Telegram app that it had hidden “dozens of hostages” in “safe places and the tunnels of the resistance.”

The militant group is said to use an underground network of defensive tunnels — called the Hamas “metro” system by the Israeli military — to travel undetected, and move weapons. The military has described the network as a “city beneath the city,” much of it under civilian infrastructure.

On Monday, Hamas’s armed wing, the Qassam Brigades, said that four Israelis being held by the militants were killed in Israeli bombardment overnight, along with the Palestinians holding them captive. The claim could not be independently verified.

How is Israel responding?

Amid widespread criticism about the lack of reliable information on the hostages, Prime Minister Benjamin Netanyahu of Israel on Sunday announced the appointment of Gal Hirsch, a retired general, as coordinator for the captives and missing.

The military and the police also opened a joint center for families to register missing relatives, asking them to bring photos and items from which they can gather DNA samples.

What happens next?

The seizure of so many hostages suggests that Hamas may want to hold them as bargaining chips for a prisoner swap, and possibly to use them as human shields as Israel strikes back in Gaza.

On Monday evening, Mr. Obeida threatened to execute a civilian hostage every time an Israeli airstrike hits Gazans “in their homes without warning.”

Thousands of Palestinians are being held in Israeli prisons, many of them convicted of security offenses or involvement in terrorism. Muhammad Deif, the leader of Hamas’s military wing, cited the detention of thousands of Palestinian militants in Israeli jails as one of the reasons for Saturday’s assault.

How have past hostage crises been resolved?

The issue of Israelis in captivity is a deeply emotional one in Israel, with the government having paid a high price in the past for the return of its citizens or of the remains of soldiers in lopsided prisoner exchange deals.

In 2006, Gaza militants seized an Israeli soldier, Gilad Shalit, and Hamas held him for five years, until he was exchanged for more than 1,000 Palestinian prisoners, many of them convicted of deadly terrorist attacks against Israelis. Hamas has also been holding the remains of two Israeli soldiers killed in a 2014 war as well as two Israeli civilians who entered Gaza that year by foot and are believed to be alive.

Israel’s monthlong war against Hezbollah, the Lebanese Shiite militant organization, in 2006 also began with a cross-border raid by Hezbollah and the abduction of two Israeli soldiers. The remains of the two soldiers were returned to Israel in 2008 as part of a prisoner exchange in which Israel handed over five Lebanese prisoners, including Samir Kuntar, who had been held for nearly three decades after being convicted in connection with a notorious attack.