Amnesty International says that shortly after sunrise on Tuesday, security forces turned up at the home of its Turkey country chairman, brought him to his office, then took him into custody.
The detention of Taner Kiliç is part of a massive crackdown on people accused of having links to cleric Fethullah Gulen started after last July's failed coup attempt. Turkish authorities blame the attempt on the U.S.-based cleric, who has denied involvement. Critics see the accusations as a pretext for silencing opponents.
"The fact that Turkey's post-coup purge has now dragged the Chair of Amnesty International Turkey into its web is further proof of just how far it has gone and just how arbitrary it has become," said Amnesty Secretary General Salil Shetty. "Taner Kiliç has a long and distinguished record of defending exactly the kind of freedoms that the Turkish authorities are now intent on trampling."
Amnesty says police also detained 22 other lawyers in the western coastal city of Izmir.
Kiliç has served as the chair of Amnesty International Turkey since 2014 and has been involved in its board since 2002.
Amnesty says the detention does not appear to be connected to the organization's work. "The detention order refers to an investigation into suspected members of the 'Fethullah Gülen Terrorist Organization,' the London-headquartered rights group said. "It is currently unclear why Kiliç is suspected of having these links."
U.S. State Department spokesperson Heather Nauert says in a statement that Kiliç is "the latest in a series of respected human rights defenders, journalists, academics, and activists detained in Turkey. These detentions, often with little evidence or transparency, are an alarming trend."
Since last year's failed coup attempt, Turkish authorities have arrested an estimated 50,000 people, The Associated Press reported. An additional 100,000 public sector workers have been dismissed from their jobs, Amnesty International reported last month. At least 130 media outlets have been shuttered and 150 journalists detained during the purges, according to Reuters.
Turkish authorities did not immediately officially comment on Kiliç's detention. They "detained 60 soldiers on Wednesday and issued detention orders for another 128 people" on suspicion of links to Gulen, Reuters reported, citing local media.
A referendum in April, which passed by a narrow margin, radically expanded the powers of Turkish President Recep Tayyip Erdogan.