Israeli and Hamas officials quarreled over the final details of a cease-fire deal that would pause the war in Gaza, underscoring the agreement’s fragility as mediators worked to ensure that it would go into effect on schedule on Sunday.

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

Hamas has reneged on parts of the Gaza ceasefire and hostage-release deal that was already agreed upon, and is creating a last-minute crisis that prevents the completion of the accord, Israeli Prime Minister Benjamin Netanyahu’s office said.