Reports on Monday said that police forces, who arrived at the villas in the morning, have been conducting searches in the villas and surrounding properties, about 100km southeast of Istanbul.

The two villas reportedly have large gardens and wells. Police dogs and drones are being used in the search ordered by Istanbul prosecutor's office. Firefighting vehicles are reported to be at the scene as well, Al Jazeera reported.

One of the villas belongs to a Saudi businessman, local media reports said.

Khashoggi - a writer, US resident and Washington Post columnist - had entered the Saudi consulate in Istanbul on October 2 to obtain documentation certifying he had divorced his former wife so he could remarry. He has not been seen since then.

After weeks of repeated denials that it had anything to do with his disappearance, Saudi Arabia eventually acknowledged that its officials were behind the murder. The whereabouts of his body are still unknown.

Turkish police have already searched the consulate and consul general's residence during the investigation they have been carrying out on the case.

Saudi Arabia and Crown Prince Mohammed bin Salman, in particular, have been facing intense global criticism over the killing of Khashoggi.

The murder of the journalist, who was critical of Prince Mohammed, also known as MBS, has tipped the kingdom into one of its worst crises.

Khashoggi was killed and reportedly dismembered in what Saudi Arabia described as a "rogue" operation, but a CIA assessment leaked to the US media pointed the finger at the crown prince - an allegation Riyadh denies.

Despite the global backlash, US President Donald Trump said earlier this week that the CIA report lacks evidence for putting blame on Prince Mohammed for the journalist.

Saudi Arabia has warned that any criticism of the crown prince would amount to crossing a "red line".

On Wednesday, Saudi Foreign Minister Adel al-Jubeir said that calls for the crown prince to be held accountable for Khashoggi's killing would not be tolerated.