President Trump broke with his own intelligence agencies on Friday, appearing to accept Saudi Arabia’s explanation that the journalist Jamal Khashoggi was killed by accident during a fistfight, while the United States’ spy agencies are increasingly convinced that he was assassinated on high-level orders from the Saudi royal court.

Mr. Trump, who has cultivated Crown Prince Mohammed bin Salman and made Saudi Arabia the linchpin of his Middle East strategy, has been deeply reluctant to point a finger at the prince, despite evidence linking him to Saudi operatives who entered the country’s consulate in Istanbul the same day that Mr. Khashoggi disappeared there.

Asked during a visit to an Air Force base in Arizona whether he viewed the Saudi explanation as credible, Mr. Trump said, “I do.”

The president said he still had questions for Prince Mohammed, and he called the killing of Mr. Khashoggi “unacceptable.” Mr. Trump also raised the possibility of sanctions against Saudi Arabia, but said that he hoped that Congress would not try to block billions of dollars in weapons sales to the kingdom, which he has held up as proof of the fruits of the alliance.