The deal, mediated by the United States, offered a glimmer of hope in a conflict that has taken an immense human toll.

The dispute underscores the fragility of the deal as mediators worked to ensure that it would go into effect on schedule.

Israeli Prime Minister Benjamin Netanyahu’s office alleged that Hamas had backed out on parts of a Gaza ceasefire and hostage deal agreed Wednesday, potentially delaying a truce between the two sides that was set to go into effect on Sunday—a day before President-elect Donald Trump takes office.