President Joe Biden said Friday that he believes putting conditions on military aid to Israel is a "worthwhile thought", and he hopes the Gaza ceasefire will last longer than four days.

Speaking to reporters from Nantucket, Massachusetts, Biden said he was encouraged by the release of some of the hostages and hopes for more.

"We expect more hostages to be released tomorrow, and more the day after, and more the day after that," he said.

The freed hostages included 13 Israelis, 10 people from Thailand and one from the Philippines, according to Qatar, which was instrumental in brokering the deal to stop fighting. In return, Israel freed 39 Palestinians from prison.

Biden said that conditioning military aid to Israel was a "worthwhile thought, but I don't think if I started off with that we would have ever gotten where we are today".

He didn't give any examples of possible conditions.