The armed wing of Hamas said on Saturday that it had decided to delay the second round of hostage releases until Israel is committed to letting aid trucks enter northern Gaza.
Hamas' al-Qassam Brigades added that the hostage releases would be delayed if Israel does not adhere to the agreed terms for the release of Palestinian prisoners.
Hamas was expected to release a second group of Israelis on Saturday under a deal to allow an exchange of 50 hostages for Palestinian prisoners.
An Israeli military spokesman told French TV BFM that, barring last minute changes, 13 Israeli hostages were expected to be freed Saturday, while 39 Palestinian prisoners would be released in return.
Earlier, Egyptian security sources had said they had received the names of 14 Israeli women and children from Hamas and were waiting for more details.
Egypt, which controls the Rafah border crossing through which vital aid has resumed passing into the Gaza Strip under the truce accord, also said it had received "positive signals" from all parties over a possible extension of that deal.
Hamas freed a total of 24 hostages on Friday - 13 Israelis, 10 Thai farm workers and a Filipino - and Israel later released 39 Palestinian women and teenagers from detention.