Turkish authorities have an audio recording which indicates that missing Saudi journalist Jamal Khashoggi was killed in the Saudi consulate in Istanbul, a Turkish official and a security source said on Monday.

"Turkish police have an audio recording that indicates that Khashoggi was killed in the Saudi consulate", the security source told Reuters. He gave no further details.

Saudi Arabia has strongly denied killing Khashoggi, a critic of the kingdom's policies. Its interior minister has described the assertion as "lies". Saudi officials have said he left the consulate shortly after entering it.

The Turkish official said evidence showing that Khashoggi had been killed was being shared with countries including Saudi Arabia and the United States.

Khashoggi, a Washington Post columnist and US resident, has not been seen since entering the consulate on October 2 to obtain documents for his forthcoming marriage. His fiancée said he never left the building.

"Evidence has been conveyed to all sides very clearly," the security source said. "Now we are at the stage of collecting concrete evidence at the consulate."

A security ofiicial holds barriers during the arrival of Saudi officials to the Saudi Arabia's consulate in Istanbul.