Turkey's president says he's personally "chasing" the investigation into the disappearance of Saudi journalist Jamal Khashoggi, whom he called a friend.

On Monday, President Recep Tayyip Erdogan said Turkish officials are investigating "everything in this matter." That includes asking for permission to search Saudi Arabia's consulate in Istanbul and requesting that the country's ambassador cooperate with the investigation.

Erdogan also said Saudi Arabia should provide evidence, such as surveillance footage, that Khashoggi left its Istanbul consulate safely.

The journalist was reportedly last seen entering that building about a week ago.

Khashoggi, a former Saudi government adviser, has used his column  in The Washington Post  to criticize Crown Prince Mohammed bin Salman.

Unnamed officials have  told several news outlets  a group of Saudi nationals killed Khashoggi inside the consulate, but Saudi Arabia  has denied the allegation .  Additional reporting by  Newsy affiliate CNN .