The Saudi leaders “assured me that they will conduct a complete, thorough investigation of all of the facts surrounding Mr. Khashoggi and that they’ll do so in a timely fashion,” Mr. Pompeo said in remarks to reporters at the White House after he briefed the president about his meetings in Riyadh. He said the Saudi report would be “transparent for everyone to see, to ask questions about and to acquire.”

Typically reports involving national security matters are highly redacted, if they are released at all. Mr. Pompeo also reminded journalists of America’s long “strategic” relationship with the Saudis, dating back to 1932, and he said the kingdom remained an “important counterterrorism partner.”

After so many other executives and foreign officials scrapped plans to attend the conference, Mr. Mnuchin’s attendance emerged as a litmus test for America’s commitment to human rights. Mr. Trump and Mr. Pompeo have emphasized that the strategic economic relationship between the United States and Saudi Arabia goes back decades, and that it should not be upended by the disappearance of Mr. Khashoggi.

Mr. Trump has also been focused on the fact that the Saudis are spending hundreds of millions of dollars to purchase American-made military equipment and has said he does not want to do anything that could cost American jobs.

Former Treasury officials and friends of Mr. Mnuchin have been watching closely to see if he would change his mind about the conference and several have spoken candidly about his need to withdraw.

As the news media described gruesome audio recordings that purport to depict the dismembering of Mr. Khashoggi, Mr. Mnuchin faced backlash from Republican lawmakers such as Senator Marco Rubio of Florida and Senator Jeff Flake of Arizona, as well as several top Democrats.

Former Treasury Secretary Paul H. O’Neill, who served during the George W. Bush administration, called the idea of Mr. Mnuchin attending “ridiculous” under the circumstances.