The Washington Post, whose columnist Jamal Khashoggi was reported to have been killed in the Saudi consulate in Istanbul, has accused the administration of US President Donald Trump of performing a “diplomatic cleanup operation” for Riyadh.

In an editorial headlined “Why is the Trump administration cleaning up Saudi Arabia's mess?” the paper backed calls by UN officials for an independent international commission into the disappearance of the journalist earlier this month, which has tarnished the image of Crown Prince Mohammed bin Salman.

US Secretary of State Mike Pompeo was sent to Riyadh on Tuesday, according to the administration, to press the Saudi leadership to get to the bottom of the case.

But Pompeo, “who smiled broadly as he greeted Crown Prince Mohammed bin Salman, appeared less intent on determining the truth than in helping the de facto Saudi ruler escape from the crisis he triggered,” said the Post.

Read: ‘This has not been business as usual in my country’: excerpts from Saudi journalist Khashoggi’s writings

“The best metaphor for Mr Pompeo's diplomacy seemed to be what reporters witnessed outside the Saudi Consulate in Istanbul, where Mr Khashoggi was last seen Oct. 2: the arrival of a cleaning crew with buckets, mops and fluids.” Trump, it added, had “signaled that he is more than ready to assist in that dodge.

“The president tweeted that in a phone call, the young Saudi leader had 'totally denied any knowledge of what took place' — as if that should settle the matter.”

The Post, which is generally critical of Trump and is frequently attacked by the president in return, added that the case should be investigated by the UN's Security Council or Human Rights Council.

“Until the full truth about Mr Khashoggi is disclosed, US businesses should shun the Saudi regime and Congress should block all military sales,” it added.

Trump on Wednesday denied he was covering for the longtime US ally.

“No not at all, I just want to find out what's happening,” he told journalists in the White House.

“I'm not giving cover at all,” he said, adding that he would be getting a “full report” on the affair from Pompeo by the end of the week.