Local Amnesty director Idil Eser is one of 10 activists, including a German and a Swedish national, who have been accused of aiding terror organisations.
A Turkish court remanded the local director of Amnesty International and five other human rights activists in custody on Tuesday on various charges, ranging from helping terror groups and being in communication with their affiliates.
Turkey's state prosecutor had asked the court on Monday to extend the detention of 10 activists pending trial on suspicion of links to the network of US-based cleric Fethullah Gulen, whom Ankara blames for last year's attempted coup.
The ruling came a day after the activists, who have not yet been formally charged, gave statements to prosecutors at an Istanbul court for the first time since their detention on July 5.
Amnesty's Turkey director, Idil Eser, a German national and a Swedish national were among 10 activists who were detained. The activists were taken as they attended a workshop on digital security and information management at a hotel on an island near Istanbul, the rights group said.
"Six were remanded in custody and four released on judicial control," Amnesty's Turkey researcher Andrew Gardner told AFP.
Prosecutors accuse them of "committing a crime in the name of a terror organisation without being a member," he said.
Gunal Kursun, Ozlem Dalkiran, Veli Acu of the Human Rights Agenda Association, Ali Garavi and Peter Steudtner are among the six who were remanded in custody along with Eser.
Nalan Erkem, Seyhmus Ozbekli, Nejat Tastan and Ilknur Ustun of the Women's Coalition were released on judicial control.
Turkey's President Recep Tayyip Erdogan said "Those ones that you asked, why did they gather at that hotel in that island? Unfortunately, they gathered there for a meeting which is, virtually, a continuation of 15th of July (coup attempt)."
German Chancellor Angela Merkel on Tuesday criticised Turkey's detention of German human rights activist Peter Steudtner as "absolutely unjustified". Merkel said the German government would do all it could to secure his release.
Amnesty International said on Tuesday critics of the government in Turkey "are no longer safe".
Ankara blames Gulen and the Fetullah Terrorist Organisation (FETO) for orchestrating the attempted coup which killed at least 249 people and wounded more than 2,000.