Germany's domestic intelligence agency BfV has warned about Turkey's increased espionage activities in Germany, amid souring relations between the two countries ahead of a Turkish referendum to boost the power of the president.
"The BfV is observing a significant increase in intelligence efforts by Turkey in Germany," said the agency in a statement on Wednesday.
In January, Berlin launched an investigation into allegations of espionage by Turkish clerics working in religious centers across Germany. Prosecutors suspected that the clerics received direct orders from a governmental organization responsible for religious affairs in Turkey.
The BfV provided no further details on the alleged spying activities but said widening divisions in Turkey over the upcoming referendum had clearly been mirrored in Germany.
Germany is home to more than three million ethnic Turks, the largest population of expats outside Turkey.
About half of the Turks in Germany have the right to vote in the April 16 referendum, which aims to boost the authority of President Recep Tayyip Erdogan.
Berlin has ordered the cancelation of a number of rallies related to the referendum in Germany attended by Turkish government officials, saying Ankara could not use the German soil to promote a specific political agenda. The cancelations have affected the already-strained ties between the two sides.
The German government has been a vocal critic of Erdogan's massive crackdown on those believed to have played a role in a coup attempt in Turkey in July last year. More than 40,000 have been arrested and over 110,000 have been discharged from their jobs in the crackdown. Germany says Turkey has acted beyond the rule of law.
Turkey has accused Germany of not doing enough to condemn the coup and says Berlin continues to protect elements linked to an outlawed Kurdish militant group working against the Turkish government.
The relations have hit a fresh low in recent weeks in the wake of Turkey's arrest of a German-Turkish journalist over spying allegations.
Deniz Yucel, a correspondent for the German daily Die Welt, was detained after he reported on hacked emails of a Turkish minister who happened to be Erdogan's son-in law.
A spokesman for the German Foreign Ministry said on Wednesday that Ankara should provide Berlin with consular access to Yucel.
"Of course it is imperative for us to now establish consular contact with Mr. Yucel and to speak to him ourselves," said the official at a regular government news conference in Berlin.
German Chancellor Angela Merkel and other top-ranking officials in Germany have called on Turkey to release Yucel without any delay. Ankara says it has the right to hold the journalist pending trial under a state of emergency law introduced after the abortive coup.