Talks with Israel through mediators on further steps in a ceasefire agreement are conditional on Palestinians being released as agreed, Hamas official Basem Naim said on Sunday.
Israel said on Sunday it was delaying the release of hundreds of Palestinians held in detention it had planned to free the day before until militant group Hamas met its conditions.
Prime Minister Benjamin Netanyahu's office said Israel was waiting to deliver the 620 Palestinian prisoners and those held under administrative detention "until the release of the next hostages has been assured, and without the humiliating ceremonies".
The White House on Sunday backed Israel's decision to delay releasing the Palestinians, citing the "barbaric treatment" of Israeli hostages by Hamas.
That was a reference to recent handovers by Hamas that United Nations officials said went against international law because they were not respectful.
The delay was an "appropriate response" to Hamas' treatment of the hostages, a statement from the United States National Security Council spokesperson Brian Hughes said.
US President Donald Trump has said he is prepared to support Israel in "whatever course of action it chooses regarding Hamas".
Hamas has made hostages appear on stage in front of crowds and sometimes speak before they were handed over. Coffins with hostage remains have also been carried through crowds.
"Any talks with the enemy through mediators regarding any upcoming steps are conditional on the release of the 620 Palestinian prisoners agreed upon in exchange for the four bodies and the six Israeli captives who were freed on Saturday," Naim told Reuters.
"The mediators must ensure that the enemy adheres to the terms of the agreement as stated in the agreed-upon text," Naim said.
The Palestinian Prisoner's Society, a local group that supports Palestinian prisoners, said Israel is practising "state terrorism against the prisoners and their families".
Ghasan Washahi, whose brother was set to be released on Saturday, said his family was disappointed with the delay.
"Every time there was a list of prisoners set to be released, we would wait, hoping Islam's name would be among them, but it was never there," he said, referring to his brother.
"My mother even started losing hope that he would be freed in the deal. And when his name finally appeared, Israel halted the deal."
Israel and Hamas have frequently accused each other of violations since the ceasefire started on 19 January, but it has so far continued to hold. Hamas at one stage said it would stop handing over hostages because of alleged Israeli breaches.
The ceasefire has brought a pause in the fighting, but prospects of a definitive end to the war remain unclear.
Both sides have said they intend to start talks on a second stage, which mediators say aims to agree on the return of all remaining hostages and the full withdrawal of Israeli troops.
The conflict escalated when Hamas-led militants launched a cross-border attack on Israeli communities on 7 October 2023 that killed 1,200 and resulted in 251 people being taken hostage, according to Israeli tallies.
The subsequent Israeli offensive has killed at least 48,000 people, according to Palestinian health authorities, and reduced much of the enclave to rubble, leaving some hundreds of thousands in makeshift shelters and dependent on aid trucks.
