US Secretary of State Mike Pompeo has met King Salman in Saudi Arabia, as pressure grows on the Saudis to explain the fate of journalist Jamal Khashoggi.
Mr Khashoggi was last seen at the Saudi consulate in Istanbul two weeks ago.
Turkish officials believe Mr Khashoggi was murdered by Saudi agents but the Saudis have denied this.
However, US media are reporting that the Saudis may be preparing to admit that Mr Khashoggi died as a result of an interrogation that went wrong.
Overnight, Turkish police completed a search of the consulate after being admitted by Saudi authorities.
The secretary of state has now begun talks in Riyadh, looking for the king to expand on his conversation with President Donald Trump on Monday.
Tweeting about the call, Mr Trump said: “Just spoke to the king of Saudi Arabia who denies any knowledge of whatever may have happened ‘to our Saudi Arabian citizen’.”
He later told reporters: “The denial was very, very strong. It sounded to me like maybe these could have been rogue killers. Who knows?”
There is a lot at stake given the strength of Saudi-US ties. Mr Trump has already ruled out cancelling a lucrative arms deal, although he did threaten “severe punishment” if the kingdom were found to be responsible for the death.
King Salman ordered an investigation into the missing journalist on Monday.
Saudi statements up to now have dismissed allegations of a killing as “baseless” and “lies”.
The kingdom has also angrily rejected what it called political and economic “threats”, saying it would respond to any punitive action, such as sanctions, “with a bigger one”.
Reflecting the growing pressure on Saudi Arabia, UN High Commissioner for Human Rights Michelle Bachelet on Tuesday demanded that the kingdom and Turkey reveal all that they know about the case.
She said that the diplomatic inviolability of the consulate and the diplomatic immunity of officials should be waived during the investigation.