Prosecutors have asked for jail sentences of between 7.5 and 15 years for a group of 11 rights activists being held on terror-related charges, Turkey's Dogan news agency reported on Sunday.

Most of the accused — including German citizen Peter Steudtner, his Swedish colleague Ali Gharavi, and Amnesty International's Turkey Director Idil Eser — were arrested on July 5 at a human rights workshop near Istanbul.

According to Dogan, they have been charged with "giving help to an armed terror group" in a 17-page indictment, signaling the first step in court proceedings.

The charges relate to alleged communications with suspects linked to Kurdish militants and the movement led by US-based Muslim cleric Fethullah Gulen, whom Ankara believes orchestrated last year's failed coup. Gulen has denied the accusations.

Germany's foreign minister, Sigmar Gabriel, said he was very worried about the latest development.

"The demand for up to 15 years in prison is totally incomprehensible to us and not acceptable," Gabriel said in a statement, adding Berlin had been in contact with Ankara about the matter.

Thousands rounded up amid crackdown

Tens of thousands of people have been arrested in Turkey in the wake of the July 15, 2016 coup attempt, sparking international concerns about the deterioration of democracy and free speech under increasingly authoritarian President Recep Tayyip Erdogan.

Steudtner is not the first German to be caught up in the post-coup crackdown. According to the German government, there are 11 Germans in custody in Turkey for political reasons, including journalists Deniz Yucel and Mesale Tolu.

In an interview with German magazine Spiegel on Sunday, Turkish Foreign Minister Mevlut Cavusoglu said that he would push for Steudtner's case to be sped up.

The arrests have stoked tensions with Berlin, with one German minister comparing Ankara's behavior to the authoritarian former communist East Germany.

Erdogan's government says EU critics of the case, and of the wider crackdown in the aftermath of the coup, do not understand the scale of the security challenges facing Turkey.

nm/jlw (AFP, Reuters, AP, dpa)