The tense cease-fire between Israel and Hamas appeared to be back on track early Sunday after the release of a second group of hostages held by the terrorists and Palestinian felons from Israeli prisons, but the swap followed an hourslong delay that underscored the truce’s fragility.

In a separate development, Hamas announced Sunday that one of its top commanders had been killed, without saying when or how.

The exchange was delayed Saturday evening after Hamas accused Israel of violating the agreement, which has brought the first significant pause in seven weeks of war marked by the deadliest Israeli-Palestinian violence in decades, vast destruction and displacement across the Gaza Strip, and a hostage crisis that has shaken Israel.

Qatar and Egypt, which mediate with Hamas, announced late Saturday that the obstacles to the exchange had been overcome. The terrorists released 17 hostages, including 13 Israelis, and Israel freed 39 Palestinian prisoners.

Thousands of people gathered in central Tel Aviv late Saturday to call for the release of all the estimated 240 people captured by Hamas in its October 7 rampage across southern Israel, which ignited the war. They accused Prime Minister Netanyahu of not doing enough to bring them back.

Pressure from the hostages’ families has sharpened the dilemma facing the country’s leaders, who seek to eliminate Hamas as a military and governing power while returning all the captives.

The four-day cease-fire, which began Friday, was brokered by Qatar, Egypt and the United States. Hamas is to release at least 50 Israeli hostages, and Israel 150 Palestinian prisoners. All are women and minors.

Israel has said the truce can be extended by an extra day for every additional 10 hostages freed, but has vowed to quickly resume its offensive once it ends. Israel said early Sunday that it had received a new list of hostages slated to be released later in the day, in the third of four scheduled swaps.

Hamas announced the death of Ahmed al-Ghandour, without providing further details. He was in charge of northern Gaza and a member of Hamas’ top military council, and is the highest-ranking militant known to have been killed in the fighting.

Al-Ghandour, believed to have been around 56 years old, had survived at least three Israeli attempts on his life, and helped plan a cross-border attack in 2006 in which Palestinian terrorists captured an Israeli soldier, according to the Counter Extremism Project, an advocacy group based in Washington.

Hamas said he was killed along with three other senior militants, including Ayman Siam, who Israel says was in charge of Hamas’ rocket-firing unit. The Israeli military had mentioned both men in a November 16 statement, saying it had targeted an underground complex where Hamas leaders were hiding and accusing the group of concealing their deaths.

The Israeli military has killed thousands of terrorists, including several mid-ranking commanders it has identified by name. The pause in fighting has given some respite to Gaza’s 2.3 million people and silenced the barrage of rocket attacks on Israel from the strip.

Shortly before midnight Saturday, Hamas released the second group of hostages, 13 Israelis and four Thais. They were turned over to Egypt and then transferred to Israel, where they were taken to hospitals.

Hamas released a video showing the hostages appearing shaken but mostly in good physical condition as masked militants led them to Red Cross vehicles. One girl was on crutches and wore a cast on her left foot.

The Israeli hostages freed on Saturday included seven children and six women, Mr. Netanyahu’s office announced. Most were from Kibbutz Be’eri, a community Hamas terrorists ravaged during their October 7 cross-border attack. The children ranged in age from 3 to 16, and the women ranged from 18 to 67.

All the released hostages either had a family member killed in the October 7 rampage or a loved one still in captivity in Gaza, a kibbutz spokesperson said.