Turkey on Sunday accused Germany of supporting the network of a U.S.-based Muslim cleric it blames for last year’s attempted coup, comments likely to aggravate a diplomatic feud between the two countries.

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.

On Saturday, German news magazine Der Spiegel published an interview with the head of Germany’s 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 Organisation” 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.”

There was no response from Germany to the comments.

Ankara 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 were killed in the coup attempt.

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

JAILED JOURNALIST

Kalin said there was a possibility Erdogan could plan a rally to address Turks in Germany before the April 16 referendum on changing the constitution, a move that would further heighten tensions with Berlin.

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

At a speech on Sunday in Istanbul, Erdogan lashed out against a Turkish-German journalist now in jail in Turkey, calling him a terrorist agent.

Erdogan, who was speaking at a meeting of an Islamic foundation, said the reporter, Deniz Yucel of Germany’s Die Welt newspaper, would be tried by Turkey’s independent judiciary.

Authorities arrested Yucel, a dual Turkish and German national, last month on charges of propaganda in support of a terrorist organisation and inciting the public to violence.

He was initially detained after he reported on emails that a leftist hacker collective had purportedly obtained from the private account of Berat Albayrak, Turkey’s energy minister and Erdogan’s son-in-law.

Turkey’s government has sent German authorities requests for 40 searches and three extraditions linked to supporters of Fethullah Gulen, the U.S-based Muslim cleric it blames for last month’s attempted coup, magazine Der Spiegel reported on Saturday.

Turkish President Tayyip Erdogan accuses a network of schools, charities and businesses led by Gulen, and built up in Turkey and abroad over decades, of infiltrating state institutions and orchestrating the failed coup.

Authorities in Turkey have arrested or suspended tens of thousands of police, troops, officials, judges and civil servants because of their alleged links to Gulen’s movement.

Citing classified documents, Spiegel said Turkey’s secret service had asked Germany’s foreign intelligence agency (BND) for help in rounding up Gulen supporters in Germany.

The magazine said the Turkish secret service wanted the BND to use its influence to spur German lawmakers into taking action against Gulen supporters and extraditing them to Turkey.

A spokesman for the BND said the agency only reported on the operative aspects of its work to the German government and the responsible authorities in the lower house of parliament.

A Turkish presidency official said: “It’s not our policy to comment on intelligence operations. However, we expect all our friends and allies to assist Turkey’s efforts to hold FETO operatives accountable for their crimes.” FETO is an abbreviation standing for the “Gulenist Terror Group” which is how Ankara refers to Gulen’s movement.

Germany is home to a three-million strong Turkish community and concern is growing that tensions between Erdogan backers and Gulen supporters are spilling over onto German soil.

Erdogan backers have demonstrated in several German cities since July’s attempted putsch, shops have been boycotted by political rivals and hate mail has been sent to anti-Erdogan politicians.

Turkish Prime Minister Binali Yildirim said on Saturday Ankara would put its domestic and external intelligence operations under an umbrella structure to allow better coordination and help prevent another coup attempt.