Few details about the disarmament agreement were initially released and there was no immediate word from Israeli officials or Hamas on the president's announcement.
U.S. President Donald Trump expressed concern in a social media post that too few of the dead hostages have been returned.
All 20 living hostages held by Hamas and hundreds of Palestinian prisoners held by Israel walked free Monday as part of a ceasefire pausing two years of war that decimated the Gaza Strip and killed tens of thousands of Palestinians.
Responding to a question about reports of Hamas rearming themselves, Trump said that "we gave them approval for a period of time."
The moment remains fragile, with Israel and Hamas still in the early stages of implementing the first phase of Trump's plan.
As part of the ceasefire deal to end the two-year war, more than 1,900 Palestinian prisoners were released around the same time as the Israeli hostages.