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.

Hamas freed six hostages from Gaza on Saturday, the last living Israeli captives slated for release under the first phase of a fragile ceasefire accord, in exchange for hundreds of Palestinian prisoners and detainees.

The hostages are the last living hostages to be freed in the first phase of a fragile deal with Israel, adding to pressure for both sides to start negotiations to permanently end the war.

Israel’s security cabinet held an emergency meeting Tuesday following word from Hamas that three Israel hostages would not be released Saturday as agreed.

Hamas released six living hostages on Saturday in separate locations of the Gaza Strip. Hours later, Israel said it would delay releasing Palestinian prisoners

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.