A member of a Saudi assassination squad phoned a superior shortly after Jamal Khashoggi was murdered and told him "tell your boss" their mission had been accomplished, The New York Times reported.

Citing three people familiar with a recording of Khashoggi's killing collected by Turkish intelligence, the newspaper said while he was not mentioned by name, US officials believe "your boss" was a reference to Crown Prince Mohammed bin Salman.

US intelligence officials view the recording as some of the strongest evidence yet linking bin Salman to the murder, it said.

Maher Abdulaziz Mutreb, one of 15 Saudis sent to Istanbul to target Khashoggi, made the phone call and spoke in Arabic, sources told the Times. Mutreb is a security officer who frequently travels with the crown prince.

Turkish intelligence officers told US officials they believe the call was made to one of bin Salman's close aides.

"The deed was done," Mutreb told the aide, though the paper noted exact translations into English may differ.

'Pretty incriminating'

Turkish officials have said the audio recording does not conclusively implicate bin Salman, but analysts say it's an important clue.

"A phone call like that is about as close to a smoking gun as you are going to get," Bruce Riedel, a former CIA officer now at the Brookings Institution, was quoted as saying. "It is pretty incriminating evidence."

Saudi officials denied the crown prince "had any knowledge whatsoever" of Khashoggi's killing.

Referring to Mutreb's instructions to "tell your boss", a Saudi statement said Turkey "allowed our intelligence services to hear recordings, and at no moment was there any reference to the mentioned phrase in the recordings", the Times' reported.

Khashoggi - a Saudi writer, US resident and Washington Post columnist - entered the Saudi consulate in Istanbul on October 2 to obtain documentation certifying he divorced his ex-wife so he could remarry. He never came out. 

The whereabouts of Khashoggi's body are still unknown.

After weeks of repeated denials that it had anything to do with his disappearance, the kingdom eventually acknowledged the murder was premeditated.