ANKARA - There is a possibility that Turkish ministers could plan another rally in Germany ahead of an April 16 referendum on changing the constitution, President Tayyip Erdogan's spokesman said on Sunday, a move that could further heighten tension with Berlin.

Turkey has been locked in a feud with both Germany and the Netherlands after both countries prevented its ministers from addressing rallies of expatriate Turks, citing safety concerns.

Erdogan spokesman Ibrahim Kalin made the comment in an interview with broadcaster CNN Turk. Kalin said that "Turkophobia" was on the rise in Europe, as Ankara points out the West's mistakes, adding that Turkey remains a country friendly to international investors.

Turkey on Sunday accused Germany of supporting the network of a United States-based Muslim cleric it blames for last year's attempted coup.

On Saturday, German news magazine Der Spiegel published an interview with the head of the BND foreign intelligence agency, who said Ankara had failed to convince it that the cleric Fethullah Gulen was responsible for the coup attempt.

"Turkey has tried to convince us of that at every level but so far it has not succeeded," Bruno Kahl was quoted as saying.

President Tayyip Erdogan's spokesman said Kahl's comments were proof Germany was supporting Gulen's network, which Ankara refers to as the "Gulenist Terrorist Organization" or "FETO".

"It's an effort to invalidate all the information we have given them on FETO. It's a sign of their support for FETO," Ibrahim Kalin told broadcaster CNN Turk.

"Why are they protecting them? Because these are useful instruments for Germany to use against Turkey."

Germany and Turkey have been locked in a deepening row after Berlin banned some Turkish ministers from speaking to rallies of expatriate Turks ahead of a referendum next month, citing public safety concerns.

The constitutional change would give Erdogan sweeping powers. Critics say it would give him too much power.

The Turkish government blames Gulen's network of followers in the military for the abortive putsch in July, when a group of rogue soldiers seized tanks, helicopters and war planes to attack parliament and attempt to overthrow the government. More than 240 people died in the attempt.

Gulen, a former Erdogan ally who has lived in self-imposed exile in the US since 1999, has denied the charges and condemned the coup.

On Saturday, around 9,000 Kurdish supporters demonstrated in the German city of Frankfurt against Erdogan and the referendum.

Police said the demonstration was peaceful.