A ceasefire between Israel and Hamas took hold at the Gaza Strip on Sunday, ushering in an initial six-week period of calm and raising hopes for the release of dozens of hostages and an end to a devastating 15-month conflict. A last-minute delay by Hamas put off the start of the truce by nearly three hours and highlighted its fragility.

Israel said the first three hostages have arrived back in Israel and are being treated by medics before being returned to their families. The truce, which started at 11:15 a.m. local time, is just the first step toward ultimately ending the conflict and returning nearly 100 hostages abducted and still held by Hamas terrorists.

Romi Gonen, 24, Emily Damari, 28, and Doron Steinbrecher, 31, were released Sunday afternoon local time. Ms. Gonen was abducted from the Nova music festival, while the other two were kidnapped from Kibbutz Kfar Aza. Ms. Damari is an Israeli-British dual citizen.

Hamas was supposed to provide the three names before the start of the ceasefire, originally planned for 8:30 a.m. Prime Minister Netanyahu said early Sunday that the militants had not lived up to that commitment and that the Israeli military would keep fighting until they did.

Hamas eventually released the names about two hours later, citing technical reasons and saying it was still committed to the agreement.

Israel’s hardline national security minister meanwhile said his Jewish Power faction was quitting the government in protest over the ceasefire agreement. Itamar Ben-Gvir’s departure weakens Mr. Netanyahu’s coalition but will not affect the truce.

In a separate development, Israel announced that it had recovered the body of Oron Shaul, a soldier who was killed in the 2014 Israel-Hamas war, in a special operation at Gaza. The bodies of Shaul and another soldier, Hadar Goldin, remained in Gaza after the 2014 war and had not been returned despite a public campaign by their families.

The ceasefire deal was announced last week after a year of intensive mediation by the United States, Qatar and Egypt.

The 42-day first phase of the ceasefire should see a total of 33 hostages returned from Gaza and hundreds of Palestinian terrorists and detainees released. Israeli forces should pull back into a buffer zone inside Gaza, and many displaced Palestinians should be able to return home.

This is just the second ceasefire in the war, longer and more consequential than a weeklong pause in November 2023, with the potential to end the fighting for good.

Negotiations on the far more difficult second phase of this ceasefire should begin in just over two weeks. Major questions remain, including whether the war will resume after the first phase and how the rest of the hostages in Gaza will be freed.

Israel’s Cabinet approved the ceasefire early Saturday in a rare session during the Jewish Sabbath, more than two days after mediators announced the deal. The warring sides were under pressure from both the outgoing Biden administration and President-elect Trump to achieve a deal before the U.S. presidential inauguration on Monday.