The Washington Post has protested the disappearance of a Saudi columnist who has contributed regularly to the paper by publishing a stark, blank page beneath his byline on Friday.

Jamal Khashoggi, a 59-year-old veteran journalist and commentator based in Washington, vanished after entering the Saudi consulate in Istanbul this week to sort out personal paperwork ahead of his marriage to a Turkish woman.

“A missing voice”, read the headline, beneath a photo of Mr Khashoggi on the phone, and above an empty space without any text.

“Jamal Khashoggi is a Saudi journalist and author, and a columnist for Washington Post Global Opinions,” read an editor’s note. “Khashoggi’s words should appear in the space above, but he has not been heard from since he entered a Saudi consulate in Istanbul for a routine consular matter on Tuesday afternoon.”

Once an insider within the Saudi elite, Mr Khashoggi fell out with the leadership following the ascent of Mohammed bin Salman, the kingdom’s ambitious 30-something crown prince. He has grown increasingly critical of the Saudi regime as the crown prince, acting under the authority of his father, King Salman, has cracked down on dissidents, including secular and religious activists, as well as rival business leaders.

A report by Saudi Arabia’s official news agency claimed Mr Khashoggi exited the consulate in the leafy Levent district of Istanbul shortly after entering.

The paper published a stark, blank block in the middle of its opinion pages to protest the disappearance of its Saudi columnist (The Washington Post)

“The consulate has confirmed that it is coordinating with the brotherly local Turkish authorities in the follow-up procedures to reveal the circumstances surrounding the disappearance of citizen Jamal Khashoggi after having left the consulate building,” Saudi SPA news agency said on Thursday.

But Mr Khashoggi’s fiancée and friends say he never left, and they believe it’s likely he remains inside the building.

Turkish authorities also reportedly sorted through closed-circuit television footage and concluded he never left. Ankara on Thursday summoned the Saudi ambassador to enquire into the whereabouts of Mr Khashoggi.

Turkish media has reported widely on Mr Khashoggi’s disappearance, adding to pressure on an Ankara government not looking for a fight with an oil-rich and influential Gulf state which has become a source of tourism and investment revenue. Karar, a left-wing newspaper, reported that the disappearance of the journalist had “stirred the world”, demanding in a headline, “Answer, Riyadh”.

Dissident Saudi journalist Jamal Khashoggi held inside Istanbul consulate

International media and human rights advocacy groups including the the New York-based Committee to Protect Journalists and the Paris-based Reporters Without Borders have spoken out on Mr Khashoggi’s behalf.

Human Rights Watch, the New York-based group, described Mr Khashoggi’s detention as part of a broader crackdown.

“If Saudi authorities surreptitiously detained Khashoggi it would be yet another escalation of Crown Prince Muhammad bin Salman’s reign of repression against peaceful dissidents and critics,” Sarah Leah Whitson, Middle East director at Human Rights Watch, said in a statement. “The burden of proof is on Saudi Arabia to produce evidence for its claim that Khashoggi left the consulate alone, and that Saudi agents have not detained him.”