President-elect Donald J. Trump said on Tuesday that “all hell will break out in the Middle East” if the hostages being held by Hamas are not released by Inauguration Day, repeating the threat four times during a wide-ranging news conference at his Mar-a-Lago estate in Florida.

“If they’re not back by the time I get into office, all hell will break out in the Middle East,” he told reporters. “And it will not be good for Hamas, and it will not be good, frankly, for anyone. All hell will break out. I don’t have to say any more, but that’s what it is.”

Mr. Trump did not elaborate about what actions he might take if the hostages were not released by the time he enters office. And he declined to provide details about what he or his advisers are doing in the days leading up to the inauguration. Officials say about 100 hostages, including some Americans, who were seized on Oct. 7, 2023, remain captive in Gaza, though they believe many of them may have died in captivity.

“They should have never taken them,” Mr. Trump told reporters. “There should have never been the attack of Oct. 7. People forget that. But there was, and many people were killed.”

President Biden and his top national security aides have been working for months to try to negotiate the release of the remaining hostages. A deal has seemed imminent several times, only to fall apart after what Biden administration officials have said were rejections by Hamas negotiators. Israeli officials have also objected to some parts of proposed deals.