Police have detained six more people following the assassination on Monday of Russian Ambassador Andrei Karlov, authorities said on Wednesday.
The latest detentions were in the western Turkish city of Izmir, bringing to 13 the number being questioned.
An off-duty riot police officer, 22-year-old Mevlut Mert Altintas, shot Karlov at the opening of a photo exhibition in the Turkish capital of Ankara.
A joint taskforce of Turkish police and an 18-member Russian team is investigating the murder.
Turkey has linked Altintas to the Fethullah Terrorist Organisation (FETO).
Turkish Foreign Minister Mevlut Cavusoglu on Tuesday told US Secretary of State John Kerry, "Turkey and Russia know that FETO is behind the attack."
The US-based head of FETO, Fethullah Gulen, has denied responsibility.
The attack came on the eve of talks between Russia, Turkey and Iran in Moscow to find a solution to the Syrian crisis.
Following the incident, Russia and Turkey said the assassination would neither harm relations between them nor the talks on the Syrian crisis.