The Hamas militant group on Thursday said US President Donald Trump's ultimatum promising more destruction in Gaza if Israeli hostages are not immediately returned threatens to upend an already fragile ceasefire agreement.

On Wednesday, Trump posted on his Truth Social platform what he called a "last warning" for Hamas's leadership to leave Gaza.

"Release all of the Hostages now, not later, and immediately return all of the dead bodies of the people you murdered, or it is OVER for you," Trump wrote. Trump also warned Gazans "you are dead" if hostages continue to be held.

"These threats complicate matters regarding the ceasefire agreement," Hamas spokesman Hazem Qasim said in a statement, adding that Trump's remarks encourage Israel to avoid implementing its terms.

The first phase of a ceasefire that started on January 19, the day before Trump took office, ended over the weekend. As fighting in Gaza has mostly been paused, Hamas has exchanged 33 Israeli hostages for around 2,000 Palestinian prisoners and detainees.

The second phase of the ceasefire calls for remaining hostages to be freed and for a final negotiation to end the conflict.

However, many sticking points remain. Hamas is demanding all Israeli forces leave Gaza. It is also unclear what postwar governance of Gaza would look like and the role Hamas would play, if any. Trump has drawn criticism for suggesting Gaza be  "emptied out" and turned into a "riviera." 

On Tuesday, Israeli Foreign Minister Gideon Saar said Israel was "ready to continue to phase two," but that "in order to extend the time or the framework, we need an agreement to release more hostages."

Israel has supported a proposal from the Trump administration calling for an extension of the first phase of the ceasefire for another six weeks. Hamas has insisted that the second phase move forward.

Omer Dostri, an Israeli government spokesperson, told Army Radio earlier this week that Hamas would have "a few days" to respond to the proposal extending phase one of the ceasefire.

"If not, the Cabinet will convene and decide on the next step," he said.

Since the first phase of the ceasefire expired, Israel has also been halting aid trucks from entering Gaza, claiming the aid is being looted and seized by Hamas.

Trump's threats come as the US increases military support of Israel, with the US expediting billions of dollars in weapons deliveries. 

Trump said he was "sending Israel everything it needs to finish the job."

Meanwhile, the US government confirmed it was holding unprecedented, direct talks with Hamas in Gaza. The White House confirmed US envoy on hostage affairs, Adam Boehler, was discussing American hostages with Hamas representatives.

White House press secretary Karoline Leavitt said Israel had been consulted on the matter, but did not share further details on the content of the talks. Up until this point, the US role in negotiating a ceasefire and hostage release has been through Israel and mediators from Qatar and Egypt.

The United States, Israel and the European Union all classify Hamas as a terrorist organization.

On October 7, more than 1,200 people were killed in the Hamas terror attacks on southern Israel that sparked Israel's military retaliation in Gaza. More than 48,000 people have been killed in the Palestinian enclave. 

Of 251 hostages taken by Hamas on October 7, an estimated 58 remain in Gaza. Israeli authorities believe fewer than half are still alive.

Edited by: Sean Sinico