A security guard stands behind barriers on a blocked road, leading to the Saudi Consulate in Istanbul on Oct. 3, 2018. (Lefteris Pitarakis/AP)

The Turkish Foreign Ministry summoned Saudi Arabia’s ambassador to discuss the whereabouts of veteran journalist Jamal Khashoggi, Turkey’s state media reported, after he disappeared while visiting the Saudi Consulate in Istanbul on Tuesday.

Ambassador Walid bin Abdul Karim El Khereiji was called to the ministry Wednesday for questions about Khashoggi’s location, the private broadcaster NTV reported from Ankara, the Turkish capital. The ambassador, who met with Turkey’s deputy foreign minister, denied having knowledge of Khashoggi’s whereabouts, Thursday’s news report said.

According to NTV, Khereiji was told that “the matter should be clarified as soon as possible.”

Turkey’s summoning of the ambassador came as the New York-based Human Rights Watch called on the Turkish authorities to intensify their investigation into Khashoggi’s whereabouts.  The journalist, who writes for The Washington Post’s Global Opinions section and has criticized the Saudi leadership over the past year, has not been heard from since he entered the Saudi Consulate on Tuesday afternoon to obtain documents for his upcoming wedding, according to his fiancee and friends.  

Turkish officials said on Wednesday that they believed he was still inside the consulate. That contradicted assertions by the Saudi government, which said that Khashoggi left the mission soon after entering. 

“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, the Middle East director at Human Rights Watch, said in a statement released Thursday, referring to Saudi Arabia’s young and influential heir to the throne.

“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,” she said.  

Khashoggi entered the consulate about 1 p.m. Tuesday, according to his fiancee, who said she accompanied him but waited outside. The fiancee, who asked that her name be withheld, called police when Khashoggi did not emerge at 5 p.m., after the consulate had officially closed for the day.  

[Opinion: Post contributor and prominent Saudi critic Jamal Khashoggi feared missing in Turkey]

Before he vanished, Khashoggi was among the Arab world’s best-known journalists and commentators. As an editor of English and Arabic-language Saudi news outlets, he was a critical source for outsiders trying to understand the often-inscrutable kingdom — even as Khashoggi himself fell in and out of favor with Saudi Arabia’s ruling circles.  

Khashoggi had lived in self-imposed exile in the United States since last year, when he left Saudi Arabia as its leadership showed signs it was becoming increasingly intolerant of dissent, and shortly before the authorities there began conducting mass arrests of critics and rivals. 

Over the past year, Khashoggi has written extensively about the growing influence of Crown Prince Mohammed bin Salman and has been critical of some of Mohammed’s policies, including arrests of women’s rights activists.

“Saudi authorities must immediately verify the whereabouts of Jamal Khashoggi,” the Committee to Protect Journalists said in a statement this week. “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.”