President Donald Trump has issued a stark ultimatum to Hamas, demanding an immediate release of all hostages by midday on Saturday.

He emphasized the critical importance of the situation, warning that “all hell is going to break out” if the group fails to return the hostages taken more than 15 months ago.

Mr Trump said the Gaza ceasefire should be cancelled if all remaining Israeli hostages are not returned by noon on Saturday.

The US president’s intervention came hours after Hamas has said it will delay the release of more hostages and accused Israel of violating their ceasefire deal, Sky News reported.

Speaking to reporters in the Oval Office late on Monday, the US president also said he might withhold aid to Jordan and Egypt if those countries do not take Palestinian refugees being relocated from Gaza, the Guardian reported.

Trump’s comments came after Hamas said it was delaying the release of hostages indefinitely over “violations” of the ceasefire deal, prompting Israel’s defence minister to put the country’s military on alert with orders to prepare for “any scenario in Gaza”.

Trump said the hostages should be released “not in dribs and drabs, not two and one and three and four and two”.

“We want them all back. I’m speaking for myself. Israel can override it, but for myself, Saturday at 12 o’clock – and if they’re not here, all hell is going to break out,” he said.

Trump indicated he had not spoken to Benjamin Netanyahu about the timeline he suggested. Asked about any concrete measures he was threatening to take to enforce his demand, Trump said: “You’ll find out. And they’ll find out too. Hamas will find out what I mean. These are sick people.”

He did not directly respond to a question on whether or not that would entail US military action.