US President Donald Trump has cautioned against rushing to blame Saudi Arabia over the disappearance of Saudi journalist Jamal Khashoggi.
He told the AP news agency that Riyadh was being treated as "guilty until proven innocent".
Trump also said that Saudi Crown Prince Mohammed Bin Salman had denied knowing what happened to Khashoggi.
Unnamed Turkish officials say a search of the Istanbul Saudi consulate gave more evidence that he was killed there.
The journalist, a critic of the Saudi leadership, was last seen alive entering the consulate on 2 October. Saudi Arabia has denied killing him and initially said he left the building unharmed, reports the BBC.
However, the New York Times reports that four of the 15 people named by the Turkish authorities as suspects in Khashoggi's disappearance have links to the crown prince, while another is a senior figure in the country's Interior Ministry.
According to the newspaper, one of the men has been photographed accompanying the royal on recent foreign visits.
The case has put Saudi Arabia under pressure from close allies.
On Tuesday, G7 foreign ministers called for Saudi Arabia to conduct a "transparent" probe into the issue.
Meanwhile, International Monetary Fund chief Christine Lagarde has become the latest high-profile figure to withdraw from a major Saudi investment conference next week following Khashoggi's disappearance.
US Secretary of State Mike Pompeo is due to visit Turkey on Wednesday, following a meeting with Saudi King Salman and the crown prince on Tuesday.
What has Prince Mohammed said?
The Saudi heir apparent wields considerable power in the kingdom and is being held responsible by many outside for whatever happened to Khashoggi.
Trump tweeted that Prince Mohammed had spoken to him on the phone and he "totally denied any knowledge of what took place in their Turkish Consulate".
The president said he "told me that he has already started, and will rapidly expand, a full and complete investigation into this matter. Answers will be forthcoming shortly".
The phone call coincided with a visit to Saudi Arabia by US Secretary of State Mike Pompeo, sent there by Trump to deal with the crisis in relations.
On Monday, Trump speculated that "rogue killers" may have been behind the journalist's disappearance.
In a further sign of disquiet within the US, a leading Republican senator and defender of US-Saudi links, Lindsey Graham, has been highly critical of the Saudi crown prince.
"This guy's gotta go," he said on Tuesday morning on Fox News, describing Prince Mohammed as a "wrecking ball".