US President Donald Trump said on Tuesday that Saudi authorities staged the "worst cover-up ever" in the killing of prominent journalist Jamal Khashoggi this month.Asked by a reporter in the White House Oval Office how the Khashoggi killing could have happened, Trump said: "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."Khashoggi's death in the Saudi consulate in Istanbul on Oct. 2 has caused global outrage and strained relations between Riyadh and Washington. Khashoggi, a critic of Saudi Crown Prince Mohammed bin Salman, was a US resident and columnist for The Washington Post.Trump's comments about the incident in recent days have ranged from threatening Saudi Arabia with "very severe" consequences and mentioning possible economic sanctions, to more conciliatory remarks highlighting the country's role as a US ally against Iran and Islamist militants, as well as a major purchaser of US arms.On Tuesday, Trump said the Khashoggi matter was handled badly by Saudi officials. "Bad deal, should have never been thought of. Somebody really messed up. And they had the worst cover-up ever," Trump said.Riyadh initially denied knowledge of Khashoggi's fate before saying he was killed in a fight in the consulate, a reaction that has met with skepticism from several Western governments, straining their relations with the world's biggest oil exporter.The kingdom has since changed parts of its official narrative about the killing, further deepening international concern.