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.
"This is not a legitimate investigation, this is a politically motivated witch-hunt that charts a frightening future for rights in Turkey", said Salil Shetty, Amnesty International's secretary general, in a statement on Tuesday.
Turkey's state prosecutor had asked the court on Monday to remand all of them in custody pending trial for membership of a terrorist organization.
Two foreign trainers, a German and a Swede, are also in jail.
Either the detainees will be released or "unfortunately, we could see the continuation of this process where the government has targeted all critical voices, in particular human rights civil society", Amnesty's Turkey researcher Andrew Gardner said.
German Chancellor Angela Merkel on Tuesday criticised Turkey's detention of German human rights activist Peter Steudtner as "absolutely unjustified".
Turkey has blamed the July 15, 2016, failed coup on followers of US -based Muslim cleric Fethullah Gulen and has branded his movement a terror organization.
Earlier this month, European Parliament has advised the European Union to freeze accession talks with Turkey amid growing concerns over declining human rights, media freedoms and rule of law issues in Turkey.
Erdogan declared a state of emergency days after the coup and launched a widespread purge of state institutions, arresting 50,000 people and firing 100,000 from government jobs.
"In Turkey, the judiciary is far away from being objective and independent", said Sezgin Tanrikulu, a former human rights lawyer and legislator from the CHP. "This is a moment of truth, for Turkey and for the worldwide community", he added.
Eight of those detained were Turkish rights activists, including Ilknur Ustun of the Women's Coalition and Veli Acu of the Human Rights Agenda Association.
"The global community needs to be engaging with Turkey and articulating this relationship with Turkey as what it is: a relationship with an increasingly rogue and unreliable partner", he said.
Turkey said the activists were detained after a tip-off that they were working against the government, with Erdogan comparing them to plotters in last year's failed July coup.