The Turkish Foreign Ministry summoned the Saudi ambassador in Turkey after a dissident journalist entered the Saudi consulate in Istanbul on Tuesday and vanished.

Jamal Khashoggi, a harsh critic of his country's ambitious Crown Prince, has been missing for over 48 hours.

An official from the Turkish Foreign Ministry said the Saudi ambassador was "invited" to the ministry on Thursday.

The envoy claimed that the kingdom had no information about the reporter's disappearance and that the consulate was looking into the matter.

Turkish broadcaster NTV reported that the ambassador also said during talks at the ministry that he would let officials know once he obtained information.

Turkish and Saudi authorities have given conflicting accounts about the whereabouts of the journalist.

Mr Khashoggi moved to Washington from Saudi Arabia last year, fearing retribution for his views.

The reporter previously had a friendly relationship with the country's government, particularly under the rule of the late King Abdullah bin Abdulaziz Al Saud.

But the 59-year-old had been in self-imposed exile ever since the ascent of Mohammed bin Salman, the powerful Saudi prince who has introduced a string of political and social reforms in the country and overseen a harsh crackdown on dissidents and rival royal family members.

Mr Khashoggi served for years as editor-in-chief of the Saudi daily newspaper Al-Watan, appeared regularly on television and contributed to The Washington Post.

He visited the consulate in the Levant district of Istanbul on Friday, to finish some paperwork ahead of his marriage to his Turkish fiancee.

The journalist was told to return on Tuesday at 1:30 pm.

His fiancee, Hatice, took his valuables and electronic devices before he returned to the embassy. Hours passed and she grew alarmed as he failed to emerge from the building.

She began to panic and called Mr Khashoggi's friends.

"I don't know what has happened to him. I can't even guess how such a thing can happen to him," Hatice told The Associated Press.

"There is no law or lawsuit against him. He is not a suspect, he has not been convicted. There is nothing against him. He is just a man whose country doesn't like his writings or his opinions."

The Washington Post said that it was extremely concerned about Mr Khashoggi's disappearance.

"We have reached out to anyone we think might be able to help locate him and assure his safety, including U.S., Turkish and Saudi officials," the newspaper's editorial page editor Fred Hiatt said in a statement.

Officials inside the consulate claim that Mr Khashoggi left the building before he vanished. Turkish police reviewed footage from security cameras and said that the journalist had not exited the consulate.

"According to the information we have, this person who is a Saudi citizen is still at the Saudi Consulate in Istanbul," a spokesman for Turkish President Recep Tayyip Erdogan told reporters on Wednesday

"We don't have information to the contrary."

Turkish police have launched an investigation into the journalist's disappearance, the Sozcu newspaper website reported on Thursday.

The Saudi consulate in Istanbul said that it is "carrying out coordination with brotherly Turkish local authorities and is following up in order to reveal the truth about the conditions of Khashoggi’s disappearance after he left the consulate building," according to a statement posted on its Twitter account in Turkish.

The journalist's disappearance threatens to further damage relations between Saudi Arabia and Turkey. The countries are on opposing sides of an ongoing four-nation boycott of Qatar.

Fears are also growing that Mr Khashoggi's apparent detention could signal a new level of brazenness from Saudi security forces, who may be seeking to silence dissent at home and abroad.

Officials in Saudi Arabia recently arrested Essam al-Zamel, an economist who criticised the Crown Prince's financial plans, on treason and terrorism charges.