President Trump said on Monday that he could cut aid to Jordan and Egypt if they refused his demand to permanently take in most Palestinians from Gaza, substantially increasing the pressure on key allies in the region to back his audacious proposal to relocate the entire population of the territory in order to redevelop it.

“If they don’t agree, I would conceivably withhold aid,” Mr. Trump told reporters in the Oval Office a day ahead of a meeting with King Abdullah II of Jordan.

Both Jordan and Egypt have rejected any suggestion that Palestinians be relocated to their countries.

Mr. Trump doubled down on the idea of forced displacement of roughly two million Palestinians, a move that some scholars have said would amount to a war crime and ethnic cleansing. In an interview with Fox News broadcast on Monday, Mr. Trump said he did not envision Palestinians who left Gaza to make way for the redevelopment plan ever returning.

Asked in the interview whether the Palestinians would eventually “have the right to return” to Gaza after his proposed construction projects had been completed, the president said, “No, they wouldn’t.”

As for where they might go, he said: “I think I could make a deal with Jordan. I think I could make a deal with Egypt.”