Israeli Defense Forces' Chief of Staff Lt. Gen. Herzi Halevi said the military will immediately return to striking the Gaza Strip once the ceasefire with Hamas ends. Halevi told soldiers the ceasefire and hostage deal would not have happened without the IDF’s pressure on Hamas.

"We do not intend, do not want, and are not ready to stop this effort before we return all the hostages… it is our moral duty to bring them back,” he said. adding the IDF will use the pause in fighting to "study, to better prepare our abilities and also to rest a little."

"And we will return immediately at the end of the ceasefire to attacking Gaza, to maneuver in Gaza. We will do it to dismantle Hamas and also to create great pressure to return as quickly as possible and as many hostages as possible, down to the last one of them," he said. "We have an obligation to fight and also to risk our lives so that [Israeli citizens] can return to live in safety, and we have hostages that we will do everything to bring them home."

As he toured the Gaza Strip Saturday, Israeli Defense Minister Yoav Gallant told Israeli commanders and soldiers that its forces will not leave the Gaza Strip until all of the hostages are returned to Israel, and any future negotiations with Hamas will be carried out amid the fighting.

"We will not leave Gaza until all the hostages are brought back home. We will find the opportunity to bring [home] additional hostages; any negotiation will be held under fire," he said. "We cannot leave Gaza and stop the war until we reach a situation in which we bring back all the hostages -- because we have many more [held captive]."

Hamas announced that it will be delaying the release of Israeli hostages, accusing Israel of violating the cease-fire agreement regarding aid trucks and the agreed-upon terms for the release of Palestinians imprisoned in Israel.

The Al-Qassam Brigades -- the armed wing of Hamas -- said it had decided to delay Saturday's scheduled second round of hostage releases until Israel committed to allowing aid trucks to enter northern Gaza. Hamas was expected to release 13 Israeli hostages in exchange for the release of 39 Palestinians imprisoned in Israel on Saturday, sources told ABC News.

"The Al-Qassam Brigades decides to delay the release of the second batch of hostages until the occupation adheres to the terms of the agreement regarding the entry of relief trucks into the northern Gaza Strip, and due to its failure to adhere to the agreed-upon criteria for releasing prisoners," Al-Qassam Brigades said in a statement.

Hamas leader Osama Hamdan, who is based in Lebanon, said relief trucks that arrived in northern Gaza today were half of the number that was agreed upon.

"There are violations committed by the Israelis in implementing the terms of the truce, some of which occurred yesterday and were repeated today," Hamdan said Saturday, adding that another issue at stake was the reported shooting of two Palestinians on Friday as they tried to reach northern Gaza.

A senior Israeli political source told ABC News that Israel did not violate the agreement. The IDF said about 200 trucks carrying humanitarian aid are expected to enter Gaza today, after 200 trucks with aid entered Gaza yesterday via the Rafah crossing and delivered their cargo to international aid organizations.

The Palestinian Red Crescent said 61 trucks carrying food, water and medical supplies headed to northern Gaza on Saturday, the largest aid convoy to reach the area since the start of the war.

-ABC News' Ayat Al-Tawy, Nasser Atta, Jordana Miller

American citizens are not expected to be among the hostages released Saturday, according to a U.S. official. No Americans were released Friday in the first group.

A senior administration official said they are still "hopeful" that three Americans will be released in this four day pause.

"The president secured the release of two American citizens as the pilot to this larger release of hostages. We are early in the process that will see at least 50 women and children released during the first phase of the agreement. We are hopeful that will include three dual national women and children, who are American citizens. This will unfold over the coming days. We will not comment on individual cases as the process is underway," the official said

A mother and daughter from Illinois, Judith and Natalie Raanan, were released last month after almost two weeks in captivity.

On Friday, President Joe Biden said it’s his "hope and expectation" that Americans will be released soon. But the president said he doesn’t know the condition of all the American hostages.

-ABC News' Justin Gomez and Selina Wang

Hamas is expected to release 13 Israeli hostages in exchange for Israel freeing 39 Palestinian prisoners Saturday as part of an ongoing swap during a four-day cease-fire, sources told ABC News.

Egyptian officials have released the same numbers, saying Egypt has received a list of 13 hostages held by Hamas in Gaza and 39 Palestinians imprisoned in Israel planned to be released Saturday.

Egypt is currently holding intensive talks with the Palestinian and Israeli sides to "secure the release of a larger number" of captives in Gaza and Palestinian prisoners, the head of the State Information Service Diaa Rashwan said.

Earlier, the Israel Prison Service said that it received a list of 42 Palestinian prisoners to be released today -- as part of the agreement between Israel and the Hamas terror group, three prisoners are to be freed for each Israeli let go. Israel said Friday it received the list of abductees who are to be released today following the schedule.

It was not immediately clear if any non-Israeli captives may also be released Saturday.

The first group of Israeli hostages have been released by Hamas in the Gaza Strip and handed over to the International Committee of the Red Cross, two sources briefed on the matter told ABC News.

The sources said the Red Cross has the hostages and that the "operation" to get them home has begun.

It was expected that 13 Israeli hostages would be freed by Hamas near Gaza's border with Egypt on Friday in a prisoner exchange deal. But it was unclear exactly how many were handed over to the Red Cross.

-ABC News' Matt Gutman and Morgan Winsor