TEHRAN (Press Shia) – Turkish authorities have asked to search Saudi Arabia's consulate in Istanbul for a missing Saudi journalist who is believed to have been killed inside the building.

The request, reported by Turkish broadcaster NTV, comes after prominent journalist Jamal Khashoggi went missing after entering the consulate in Istanbul six days ago.

Turkish President Recep Tayyip Erdogan is believed to be personally following the case as he described Khashoggi as a "journalist I knew for a long time" and a "friend".

Saudi Arabia's envoy to Ankara was summoned to the foreign ministry for a second time on Sunday.

He has been asked by Turkish diplomats to be "in full co-ordination" on the matter.

A Turkish official said, "The initial assessment of the Turkish police is that Mr Khashoggi has been killed at the consulate of Saudi Arabia in Istanbul.

"We believe that the murder was premeditated and the body was subsequently moved out of the consulate."

A senior police source told online news website Middle East Eye the journalist had been "brutally murdered, killed and cut into pieces".

"Everything was videotaped to prove the mission had been accomplished and the tape was taken out of the country," the source said.

A friend of Khashoggi, Galip Dalay, told Sky News that he "personally got the news that he was killed two days ago".

Saudi authorities rejected the allegations as "baseless" and said a team of investigators had been sent to the Turkish city to help look into the case.

“I would like to confirm that…Jamal is not at the consulate nor in the Kingdom of Saudi Arabia, and the consulate and the embassy are working to search for him,” consul-general Mohammad al-Otaibi said in an interview.