WASHINGTON — President Trump on Tuesday condemned Saudi Arabia’s account of the killing of the journalist Jamal Khashoggi as “the worst cover-up ever,” and his administration warned for the first time that it would impose human rights sanctions on some of those who took part in the plot.

Mr. Trump’s criticism, and the sanctions announced by Secretary of State Mike Pompeo, attested to the mounting pressure on the White House after Turkey’s president, Recep Tayyip Erdogan, characterized the killing of Mr. Khashoggi in the Saudi Consulate in Istanbul as premeditated and “savage.”

But the president still appeared to be playing for time, complaining about how the Saudis botched the crime rather than about who was behind it, and blacklisting what are likely to be Saudi operatives rather than decision makers like Saudi Arabia’s crown prince, Mohammed bin Salman.

“They had a very bad original concept, it was carried out poorly, and the cover-up was one of the worst in the history of cover-ups,” Mr. Trump said to reporters in the Oval Office.