U.S. and Arab mediators made significant progress overnight toward brokering a ceasefire in the Israel-Hamas war and the release of scores of hostages held in the Gaza Strip, but a deal has not been reached yet, officials said Monday.

Three officials acknowledged progress has been made and said the coming days would be critical for ending more than 15 months of fighting that has destabilized the Middle East. They spoke on condition of anonymity because they were not authorized to discuss the talks.