There has been an increase in Turkish spying in Germany, according to German intelligence agency BfV, adding to tensions between Berlin and Ankara.

As reported by Deutsche Welle (DW), Germany’s international broadcaster, 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.

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

As many as 1.4m Turks living in Germany are eligible to cast their ballot in the vote.

German Foreign Minister Sigmar Gabriel met with his Turkish counterpart Melvut Cavusoglu in Berlin on March 8. While both diplomats agreed on the importance of good relations, Cavusoglu said that Germany must now “decide whether Turkey is a friend or not”.

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

In a separate report, the Reuters news agency noted that Bfv President Hans-Georg Maassen has underscored his concern over tensions between right-wing Turks in Germany and supporters of the Kurdistan Workers Party (PKK).

“There is the danger that these proxy fights between PKK supporters and nationalist, right-wing extremist Turks will escalate because there is a high, hard-hitting potential for danger in both groups,” he said.

In January, Maassen told reporters that Germany would not tolerate Turkish intelligence operations within its borders.