Turkish police have arrested eight leading human rights activists including Amnesty International's Turkey director Idil Eser in Istanbul.
Two trainers - from Germany and Sweden - were also arrested in the raid on a digital security workshop at a hotel in Buyukada.
The police raid was "blatantly without cause", an Amnesty statement said.
The group's whereabouts are unknown. Police have jailed more than 50,000 people since a coup plot a year ago.
The police action "is a grotesque abuse of power and highlights the precarious situation facing human rights activists in the country", said Salil Shetty, Amnesty International's Secretary General.
"Idil Eser and those detained with her must be immediately and unconditionally released."
The workshop was organised by Netherlands-based rights group Hivos.
Turkey remains under a state of emergency imposed by President Recep Tayyip Erdogan after rogue army officers tried to oust him in a coup on 15 July 2016.
The post-coup crackdown has targeted tens of thousands of public servants accused of supporting US-based Muslim cleric Fethullah Gulen.
The European Parliament has deplored the crackdown on Mr Erdogan's opponents in Turkey and called for a suspension of talks on it joining the EU if Mr Erdogan is formally granted sweeping new powers.
A controversial referendum in April backed constitutional changes that would turn Turkey into a presidential republic, diminishing parliament's role.
Turkey has made very slow progress towards EU membership, amid international concern about freedom and justice under Turkey's current state of emergency.
Amnesty International's Turkey chair, Taner Kilic, is also in police custody. He was arrested on 6 June with 22 other lawyers and charged with membership of a "terrorist" organisation. Amnesty called the charges "baseless".
The seven rights activists arrested with Ms Eser on Wednesday evening were named as: Ilknur Ustun of Women's Coalition; Gunal Kursun and Veli Acu of Human Rights Agenda Association; Nalan Erkem and Ozlem Dalkiran of Citizens Assembly; Nejat Tastan of Equal Rights Watch Association and lawyer Seyhmus Ozbekli.
http://www.bbc.co.uk/news/world-europe-40517184
