Turkish President Recep Tayyip Erdogan on Tuesday called for the trial in Istanbul of the Saudi suspects in the murder of journalist Jamal Khashoggi, a crime that he said was intricately planned days in advance.

Erdogan had promised that his speech in Ankara would give the "naked truth" about the killing and he gave a host of new details while still saying Turkey wanted answers to key questions, including who gave the orders.

"My demand is that 18 people be tried in Istanbul," Erdogan said in a speech to ruling party lawmakers in Ankara, referring to 18 people including security officials who have already been detained by Riyadh.

He added that "all those who played a role in the murder" had to face punishment.

Saudi Arabia said it has detained 18 Saudi nationals and dismissed six senior government officials as a result of its investigation into the killing of khashoggi in early October in the Saudi consulate in Istanbul.

Turkish and Saudi investigations have showed that Khashoggi was killed in the consulate.

Erdogan said that the murder was "planned" days in advance according to a "roadmap" set up by a Saudi team who were sent to Istanbul for the purpose. 

The surveillance system at the Saudi consulate in Istanbul was deactivated on purpose, he said.

"First they (the Saudis implicated) removed the hard disc from the camera system," Erdogan said. "This is a political murder," he added.

But Erdogan added he still wanted answers on numerous issues including "who gave orders" to the team and where the corpse is.

Erdogan said he was confident of the full cooperation of the Saudi King Salman in the probe.

Saudi authorities have vowed to conduct a transparent investigation to bring those who killed Khashoggi to justice.