US Secretary of State Mike Pompeo is to meet Saudi King Salman amid growing controversy over the fate of Saudi journalist Jamal Khashoggi.
He will then visit Turkey, where Khashoggi was last seen at the Saudi consulate in Istanbul two weeks ago. Turkish officials believe Khashoggi was murdered by Saudi agents but Riyadh has always strongly denied this.
On Monday, President Donald Trump suggested "rogue killers" could be behind Mr Khashoggi's disappearance.
The president provided no evidence to back his comment, but said that during a phone call the Saudi king had firmly denied knowing what had happened to Khashoggi.
Unconfirmed reports in the US media suggest Saudi Arabia is preparing to admit that Mr Khashoggi died as a result of an interrogation that went wrong and that the original intention had been to abduct him.
Meanwhile, Arabic channel Al-Jazeera quotes Turkey's attorney-general's office as saying it has found evidence to back claims that Mr Khashoggi was killed inside the mission.
Earlier, a Turkish security source told the BBC officials had audio and video evidence proving Khashoggi was murdered there.
The issue has strained Saudi Arabia's ties with its closest Western allies. (BBC)