Israel has delayed an expected release of hundreds of Palestinian prisoners and detainees in exchange for returned Israeli hostages “until further notice,” the Palestinian Prisoners Society said early Sunday.

In what was set to be the largest swap under January’s ceasefire agreement, six hostages were freed, but the release of some 600 Palestinian prisoners was delayed. It comes after Shiri Bibas’s body was returned by Hamas.

Hamas on Sunday said Israel has gravely endangered a five-week-old Gaza truce by delaying the release of Palestinian prisoners under the deal because of the manner it has freed Israeli hostages.The first phase of the truce ends early in March and details of a planned subsequent phase have not been agreed.