Turkish authorities have put 11 human rights activists on trial, including the chairman of Amnesty International in Turkey, Taner Kilic.
Those facing charges at Istanbul's Caglayan courthouse on Wednesday were arrested in separate police raids in June and July and include one Swede and a German national.
Idil Eser, director of Amnesty International Turkey, is also among those on trial.
Accusations include supporting groups that Turkey has proscribed as "terrorist" organisations, such as the Gulen movement, and Kurdish separatist factions.
If convicted, the activists could face up to 15 years in prison.
The Gulen movement, led by exiled Turkish religious leader, Fethullah Gulen, is accused by Turkey's authorities of plotting a failed military coup in July 2016, which left around 300 people dead.
In its aftermath, authorities launched a broad crackdown on anyone suspected of ties to the group.
Turkey is also fighting Kurdish separatists from the Kurdistan Workers Party (PKK) and its splinter organisations.
'No substance or foundation'
Al Jazeera's Sinem Koseoglu, reporting from outside the court building in Istanbul, said the trial had attracted the attention of human rights groups both inside Turkey and outside.
"There are many human rights representatives here to support the accused, and there is an international presence as well, including diplomats such as the German consul for Istanbul, " she said.
Those present also included opposition politicians and also a deputy in the ruling Justice and Development Party.
"The government side is asking why these human rights organisations are made up of people that are totally anti-government," Koseoglu added.
Protesters outside the building carried banners condemning the trial and what they believe to be a worsening atmosphere for freedom of expression in the aftermath of the coup.
Amnesty International says the case against Kilic is without "substance or foundation" and called for the release of all of the accused.
"These two trials will be an acid test for the Turkish justice system and will demonstrate whether standing up for human rights has now become a crime in Turkey," said Amnesty's John Dalhuisen.