Amnesty International's Turkey director detained
Idil Eser, director of Amnesty International Turkey, was among 12 people picked up by Turkish security forces, as well as activists and trainers.
The swoop took place during a "digital security and information management workshop" on Buyukada, one of the Princes' Islands off Istanbul.
Turkish daily Hurriyet said 12 were arrested in the police raid.
There is no immediate indication of what the rights activists have been accused of.
"We are profoundly disturbed and outraged that some of Turkey's leading human rights defenders, including the Director of Amnesty International Turkey, should have been detained so blatantly without cause," said Salil Shetty, Amnesty International's Secretary General.
He said they must be "immediately and unconditionally released". The whereabouts of those detained is currently unknown.
Amnesty International's Turkey chair, Taner Kilic, was detained a month ago on "baseless charges", accused of links to the alleged mastermind of the 15 July failed coup Fethullah Gulen.
Turkey remains under a state of emergency following the coup with thousands arrested in raids by security forces.
Amnesty said the seven other activists detained included Ilknur Ustun of the Women's Coalition, lawyer Gunal Kursun and Veli Acu of the Human Rights Agenda Association.
Two foreign trainers for the workshop - a German and a Swedish national - as well as the hotel owner, were also detained in the raid, it added.