Israeli officials and hostage families said that Hamas’s failure to immediately return the remains of slain hostages was a breach of the cease-fire agreement that took hold on Friday. Hamas returned four of the roughly two dozen bodies believed to still be in Gaza as part of Monday’s hostage and prisoner exchange.

The Israeli military said today that the Red Cross had been dispatched to collect several more. The government has been weighing retaliatory measures like limiting the number of aid trucks allowed into Gaza, according to diplomats and two Israeli officials.

A Hamas official said that the widespread devastation in Gaza made it difficult to retrieve the remains quickly. The Israeli government believes that Hamas knows the location of many, but not all, of the bodies, three Israeli officials told The Times.

Times reporters also spoke to 15 officials from the U.S., Israel and Arab governments about how the cease-fire deal happened. The hostages were a key change: Hamas had insisted on holding on to some of them unless Israel ended the war. But the group came to believe that was giving Israel legitimacy to continue fighting.

Khalil al-Hayya, the top Hamas negotiator, told the mediators that even though the group considered the deal unfair, its priority was stopping Israel’s bombing of Gaza.