11 activists, including local Amnesty International chiefs, on trial in Turkey

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." The defendants could face up to 15 years in prison.

Dozens of protesters gathered outside the courthouse to support the activists. Amnesty International slammed the allegations as "entirely baseless" and called on the judge to throw out the case.

"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.

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.

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.

"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.

The case, and several others, have caused concern in the West. Turkish President Recep Tayyip 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.