While tensions between Berlin and Ankara have escalated ahead of next month's referendum on Turkey's presidency, the German government said on Wednesday that there has been a significant increase in Turkish spying in Germany.

Germany's domestic intelligence agency, the BfV, said divisions in Turkey leading up to the controversial April 16 referendum on boosting the powers of President Recep Tayyip Erdogan were mirrored in Germany.

"The BfV is observing a significant increase in intelligence efforts by Turkey in Germany," it said in a statement. No further details were provided.

Called referendum rallies

Already strained relations between Germany and Turkey reached a new low this month in a row over canceled Turkish political rallies to drum up support for the impending referendum.

Some 1.4 million Turks living in Germany are eligible to cast their ballot in the vote.

Hoping to calm the storm on Wednesday, German Foreign Minister Sigmar Gabriel met with his Turkish counterpart Melvut Cavusoglu in Berlin. While both diplomats agreed on the importance of good relations, Cavusoglu said that Germany must now "decide whether Turkey is a friend or not."

More talks in the pipeline

In light of recent comments from both Cavusoglu and Erdogan, Gabriel also made it clear that in maintaining good relations "there are lines that should not be crossed."

"...And one of those is the comparison with Nazi Germany," Gabriel said.

Cavusoglu, meanwhile, said he would host Gabriel for a new round of talks in Turkey "as soon as possible."

In a bid to secure support ahead of next month's referendum, Erdogan himself is also due to hold a rally in Germany. Critics have warned, however that the proposed presidential system which seeks to expand Erdogan's powers as president would cement a one-man rule in the country.

Turkish President Recep Tayyip Erdogan plans to hold a referedum rally in the coming weeks

Concerns over right-wing Turks and PKK

Fuelled by concerns over tensions between right-wing Turks in Germany and supporters of the Kurdistan Workers Party (PKK), Bfv President Hans-Georg Maassen launched an investigation in January into possible spying by clerics sent to Germany by Ankara.

"There is the danger that these proxy fights between Kurdistan Workers Party (PKK) supporters and nationalist, right-wing extremist Turks will escalate because there is a high, hard-hitting potential for danger in both groups," Maassen said.

Although not specifically addressing the issue of Turkish spying, Maassen told reporters in January that Germany would not tolerate Turkish intelligence operations within its borders.

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Watch video 02:14 Share Increasing tensions between Germany and Turkey Send Facebook google+ Whatsapp Tumblr linkedin stumble Digg reddit Newsvine Permalink https://p.dw.com/p/2YeIc From Yucel to Gaggenau: Increasing tensions between Germany and Turkey

Echoing Maassen on Wednesday, Gabriel said following his meeting with Cavusoglu that Turkey's internal fights should not be imported into Germany.

Berlin has had its own fight to deal with in recent weeks, however, following the arrest of German-Turkish journalist Deniz Yucel.

Yucel, a journalist for the German newspaper "Die Welt," was arrested last month over allegations of terrorism propaganda, making him the first German reporter to be detained in Turkey as part of Erdogan's wide-ranging crackdown on press freedom.

The 43-year-old, who has penned several articles critical of the Turkish government's treatment of ethnic Kurds, has been in jail pending trial ever since, with Erdogan labeling him a "German agent."

ksb/jm (Reuters, AFP, dpa)