Six people, including the director of Amnesty International in Turkey, were arrested by a court order on Tuesday for "helping an armed terrorist organisation", according to the state-run Anadolu Agency news outlet.

They were among the 10 who were detained in Istanbul earlier in July during a workshop on Buyukada, an island near the city.

The group comprised eight Turkish human rights activists, one Swedish trainer and one German trainer.

The Istanbul court ordered the other four be released on the condition of judicial control.

Those arrested include Amnesty International Director Idil Eser, Gunal KurSun, Ozlem Dalkıran, Veli Acu, Ali Garavi ile and Peter Steudtner.

READ MORE: Erdogan links detained rights activists to failed coup

Those released pending trial included Nalan Erkem, Seyhmus Ozbekli, Nejat Tastan and Ilknur Ustunto.

The activists had been questioned by the prosecutor since they were taken into custody on July 5.

Turkish President Recep Tayyip Erdogan has accused them of harbouring similar intentions to the perpetrators of a failed coup attempt last year.

That claim was rebuffed by Amnesty International, the rights group that has seen two of its top Turkey officials detained in a month.

In Germany, Chancellor Angela Merkel urged Turkey to release German national Peter Steudtner, calling his detention unjust.

"We will do everything on the part of the federal government, at all levels, to obtain his release," Merkel said.

"It is unfortunately another case where from our view blameless people enter the mills of justice and are thereby taken into custody."