The Washington Post has published a blank column in its Friday’s print edition and a blank page on its website to highlight the disappearance of one of its regular writers, Jamal Khashoggi, as the mystery deepens over the Saudi journalist’s whereabouts.

Khashoggi has been missing since he entered the Saudi Arabian consulate in Istanbul after midday on Tuesday. His fiancee, Hatice Cengiz, waited outside until midnight.

His visit was related to filing for a divorce, but he had reportedly expressed concerns about his safety beforehand. Turkish authorities believe he remains inside the consulate, while Saudi officials say he left the compound.

Khashoggi is one of the Arab world’s most prominent journalists and commentators. He is an outspoken critic of Saudi Arabia who has dared to defy Crown Prince Mohammed bin Salman, widely believed to the kingdom’s de facto ruler.

Washington Post Opinions (@PostOpinions) We are holding a spot for Jamal Khashoggi in Friday’s newspaper https://t.co/gBro1ilFZC pic.twitter.com/eCLKqJYHwT

The Washington Post’s editorial board has urged the prince to “do everything in his power to ensure that Mr Khashoggi is free and able to continue his work”.

In an editorial, it said: “Mr Khashoggi is not just any commentator. Over a long career, he has had close contact with Saudi royalty and knows more than most about how they think and function.

“His criticism, voiced over the past year, most surely rankles Mohammed bin Salman, who was elevated to crown prince last year and has carried out a wide-ranging campaign to silence dissent while trying to modernise the kingdom. Among those in his prisons for political speech are clerics, bloggers, journalists and activists. He imprisoned women who agitated for the right to drive, a right that was granted even as they were punished.”

Suspicions about Riyadh’s involvement in the disappearance are heightened by a number of similar incidents, including the surprise resignation of the Lebanese prime minister, Saad Hariri, last year while he was visiting Saudi Arabia. The Saudis were accused of abducting Hariri, who later suspended his resignation after leaving the kingdom.

While living in Saudi Arabia, Khashoggi was told to stop writing or posting on Twitter, where he has more than 1.6 million followers. He moved to the US more than a year ago, where he continued his commentary about his country both in print and on television.

His message struck a nuanced tone in the US, where he tried to acknowledge the reforms undertaken by Bin Salman while also highlighting the flaws.

Khashoggi previously had close links with the Saudi royal family, including having served as a media aide to Prince Turki al-Faisal, when the latter was director general of the Saudi intelligence agency.

He is also a former editor of the Saudi newspaper al-Watan and had worked with Prince Alwaleed bin Talal, a grandson of the first Saudi king who was detained last year as part of what the authorities said was an anti-corruption campaign.

Spearheaded by the crown prince, scores of wealthy businessmen – including other members of the royal family – were detained in the Ritz-Carlton hotel in Riyadh, before financial settlements with the monarchy led to their release.

In February, Khashoggi wrote in a column that restrictions on freedom of speech imposed by the crown prince had “sucked the oxygen from the once-limited but present public square. You can read, of course, but just think twice about sharing or liking whatever isn’t fully in line with the official government groupthink.”

The Committee to Protect Journalists, a New York-based NGO, urged the Saudi authorities to immediately disclose information about Khashoggi’s whereabouts. “Given the Saudi authorities’ pattern of quietly detaining critical journalists, Khashoggi’s failure to emerge from the Saudi consulate on the day he entered is a cause for alarm,” said the CPJ’s Sherif Mansour.