Saudi and Turkish officials investigating the disappearance of Saudi journalist Jamal Khashoggi are searching Saudi Arabia's consulate in Istanbul.
Turkish officials believe Mr. Khashoggi was murdered in the consulate by Saudi agents nearly two weeks ago, but Riyadh strongly denies this.
Diplomatic pressure is growing on the Saudis to give a fuller explanation.
US President Donald Trump on Monday morning tweeted that he has spoken to Saudi Arabia's King Salman King Salman, who denied knowledge of what might have happened to Mr. Khashoggi.
Mr. Trump said Secretary of State Mike Pompeo is en route to Saudi Arabia to meet the king.
The latest moves come as more leading business figures say they will not attend a major investment conference in Riyadh later this month.