Istanbul(CNN) Eleven activists have gone on trial for terror offenses in Turkey -- including two local Amnesty International chiefs and two foreigners -- as the country continues with a purge that has gutted institutions in all areas of public life.
Turkey has detained tens of thousands of people, including journalists, activists and opposition political figures, following an attempted military coup last year.
The activists are accused of aiding three groups that Turkey describes as "armed terrorist organizations" and could face up to 15 years in prison.
Amnesty International slammed the allegations as "entirely baseless."
"From the moment of their detentions, it has been clear that these are politically motivated prosecutions aimed at silencing critical voices within Turkey," Amnesty International's Europe director, John Dalhuisen, said in a statement.
Dozens of protesters gathered outside the courthouse to support the activists and called for their release.
Ten of the activists -- including Amnesty's Turkey director, İdil Eser -- were arrested in a police raid on July 5 in Istanbul while attending a workshop on wellbeing and digital security, Amnesty said. The 11th is Amnesty's Turkey chair, Taner Kılıç, who was arrested a month earlier and is being tried in an additional case.
Among the 11 are German citizen Peter Frank Steudtner, a non-violence and wellbeing trainer, and Swedish citizen Ali Gharavi, an IT strategy consultant, who join dozens of other foreign nationals detained in Turkey's purge.
The indictment alleges that the workshop was an unauthorized meeting at which the activists were orchestrating an uprising. It also alleged that the cybersecurity techniques they discussed -- such as securing information in mobile phones if the devices are seized by police and how to encrypt information -- conformed "to secrecy rules of terrorist organizations."
Amnesty called on the judge to throw out the case.
"Without substance or foundation the Turkish authorities have tried and failed to build a case against İdil, Taner and the other nine human-rights activists. It took the prosecutor more than three months to come up with nothing. It should not take the judge more than half an hour to dismiss the case against them," Amnesty said.
The rights group said that the 11 activists were carrying out standard human-rights protection activities, such as "appealing to stop the sale of tear gas, making a grant application and campaigning for the release of hunger-striking teachers."
The activists are accused of aiding the Kurdistan Workers Party (PKK) -- which is considered a terrorist organization by Turkey, the US and the EU -- and FETO, a term used by the Turkish government to describe supporters of Muslim cleric Fethullah Gulen. Gulen lives in exile in the US and Turkey blames him for orchestrating the attempted coup, which he has denied.
Kılıç is also accused in a separate case of being a member of FETO. If he is convicted, he could face 17½ years in prison.
In that case, prosecutors' evidence against Kılıç centers around his alleged downloading of ByLock, a widely available phone app used for encrypted messaging that the indictment says is also used by Gulen supporters.
Amnesty said it had commissioned two independent forensic analyses of Taner's phone that found no trace of Bylock on the device.
Wednesday's trial, and several other cases, have caused concern in the West over the erosion of civil liberties in the country under President Recep Tayyip Erdogan's rule.
Erdogan spearheaded a vote this year on constitutional change that granted him sweeping new powers that could cement his leadership until 2029.
He has overseen the extension of the country's state of emergency several times, which has allowed Ankara and the courts to continue with a crackdown that has transformed media organizations, rights groups and the country's educational institutions.