The Hamas announcement that it will delay the next planned release of Israeli hostages from Gaza has threatened a fragile truce that’s seen as having the potential to wind down 16 months of war.

A dispute over humanitarian aid has led to concerns that the cease-fire could falter before the remaining hostages are released.

Israeli Prime Minister Benjamin Netanyahu threatened to resume hostilities unless Hamas releases hostages under a ceasefire agreement on Saturday. Hamas said Monday it is delaying the hostage release.