Turkey crackdown: Rights groups outraged by latest arrests
Eight leading human rights activists arrested in Istanbul have been accused of belonging to an armed terrorist organisation.
They were attending a digital security workshop at a hotel when it was raided by Turkish police on Wednesday night.
Two trainers from Sweden and Germany were also arrested in the raid, which has been condemned by international human rights bodies.
"We don't know which terror organisation they are talking about," the activists' lawyer Selin Nakipoglu told the BBC. "All of this is very surreal."
The activists will be held for a week before facing the prosecutor.
They include the director of Amnesty International's Turkey office, Idil Eser - the second top Amnesty official to be detained in the past month.
Amnesty Turkey's chairman Taner Kilic was arrested in June on charges of having links to the Gulenists - the Islamic movement that the government accuses of masterminding the foiled coup plot a year ago. He is still in pre-trial detention.
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"The plainclothes anti-terror police raided the hotel and shouted 'Hands up!'," Ms Nakipoglu said of the latest arrests.
"These activists have been subjected to shock, fear and terror. One even thought this was part of the workshop, an exercise. All of it felt absurd."
She has been in touch with four of those detained.
"These people have spent all their lives working for human rights. They were held for 36 hours without any notice to lawyers or relatives," she said.
More than 50,000 people have been arrested since the failed coup, including more than 170 journalists and many opposition politicians, academics and activists.
President Recep Tayyip Erdogan says the crackdown is necessary to root out Gulenists. The purge of the armed forces, judiciary, police and education sector has seen more than 140,000 people dismissed from their jobs.
The Council of Europe (CoE) - the top European human rights watchdog - urged Turkey to free the eight Istanbul activists immediately.
Its Human Rights Commissioner Nils Muiznieks said he was "extremely concerned".
"I call on the Turkish authorities to immediately release those detained... and strongly urge them to stop all arbitrary interferences with the legitimate work of civil society."
Meanwhile the UN Human Rights Commissioner said the police raid "underscores our concerns that anti-terror legislation is being abused to oppress individuals trying to exercise peacefully their civil and political rights".
"We fear they are now at significant risk of torture and other cruel, inhuman or degrading treatment," UN spokeswoman Elizabeth Throssell added.
US-based Human Rights Watch called the move "a repressive new low for the Turkish state".
Turkish officials have long accused human rights defenders of engaging in covert and treasonous activities.
One pro-government daily claims the Istanbul activists were plotting an anti-government protest similar to the Gezi Park riots of 2013.
Another paper suggested the activists were spies.
Tens of thousands of people - opponents of President Erdogan - have spent 23 days marching from Ankara to Istanbul, demanding justice.
They reached Istanbul on Friday and will stage a rally on Sunday - expected to draw more than a million people.
In a controversial referendum in April, Mr Erdogan got backing for constitutional changes that will entrench his state-of-emergency powers.
Instead of being a figurehead, the president will be able to shape government policy, appoint top officials and influence the judiciary, with parliament's role diminished.