(CNN) An Austrian journalist detained in Turkey 10 days ago has been formally arrested on political charges, along with two Turkish citizens, their attorney told CNN on Friday.

Max Zirngast, Hatice Göz and Mithatcan Türetken are accused of being members of the communist organization TKP Kivilcim, according to the lawyer Tamer Dogan.

Zirngast, a left-wing Austrian journalist who lives in Ankara and has written critically about Turkish President Recep Tayyip Erdogan, was detained along with Göz and Türetken on September 11.

Zirngast was initially held for four days, and the detention was extended twice, according to Dogan. At a hearing Thursday, Zirngast described himself as a socialist who defends "universal values," according to Turkish media

"I do not carry out activities on behalf of any illegal organization," Zirngast said, according to reports.