A criminal court in Turkey extended the detention of businessman Osman Kavala as part of a probe into the 2016 defeated coup.
The court also renewed the arrest warrant for fugitive Henri Barkey, who was a former CIA advisor.
Kavala and Barkey are both accused of "violating the constitution" and conducting "political or military espionage activities."
The session was adjourned until Feb. 5.
Kavala was first arrested on criminal charges related to the 2013 Gezi protests, when small protests in Istanbul spread into nationwide demonstrations which left eight protesters and a police officer dead.
Turkey's government has said the protests amounted to a coup attempt.
He was briefly released earlier this year, but later remanded into custody by an Istanbul court as part of a probe into the 2016 defeated coup, with prosecutors accusing him of spying.
The Fetullah Terrorist Organization (FETO) and its US-based leader Fetullah Gulen orchestrated the defeated coup of July 15, 2016, which left 251 people martyred and nearly 2,200 injured.
Turkey accuses FETO of a long-running campaign to overthrow the state through the infiltration of Turkish institutions, particularly the military, police and judiciary.
