Authorities in Turkey have detained two Germans of Turkish origin in the southern city of Antalya, according to Turkey's state-run media.

Anadolu Agency said on Friday that the two Germans were taken into custody in relation to an investigation into the movement of Fethullah Gulen, a US-based Muslim leader who is accused by Ankara of masterminding a failed coup attempt last year.

Anadolu, quoting police sources, said that the duo was detained in Antalya Airport on Thursday after the police got a tip on them. The agency added that they were still being questioned.

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Many European citizens have been detained in Turkey over the past year, accused of involvement in last year's failed coup attempt on July 15, 2016 against President Recep Tayyip Erdogan.

"We're trying to establish what they are charged with," Maria Adebahr, spokeswoman for the German foreign ministry, said at a news conference on Friday.

"We must assume that it's a political charge, suspicion of terrorism, as with the others," referring to several other German citizens currently in Turkish detention

Diplomats had not been able to contact them, she added, with Friday's public holiday celebrating the Muslim Eid al-Adha festival a possible reason for delays in contacting officials.

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Around 300 people were killed during the failed coup attempt, which led to arrests as well as purges targeting tens of thousands of civil servants.

The government, which declared a state of emergency, says the purges and detentions are legitimate and aimed at removing Gulen supporters from state institutions and other parts of society.

Local and international rights groups, as well as many of Turkey's European allies, have described the measures as arbitrary, claiming that the government is using the coup bid as a pretext to silence opposition in the country.