Kern told the German newspaper "Welt am Sonntag" that Europe should protect its individual member nations from President Erdogan's outspoken drive to win over expatriate Turks ahead of April's Turkish referendum on boosting his constitutional powers.

The latest strains in EU-Turkish relations center on Ankara's arrest of German-Turkish journalist Deniz Yucel and rejections on security grounds by the German towns of Guggenau, and Frechen near Cologne, of gatherings at which visiting Turkish ministers were to have made campaign appearances.

Austria's chancellor said an EU-wide ban on Turkish politicians' campaigning inside Europe would ease Turkish pressure on individual EU nations such as Germany.

"A joint approach by the EU to prevent such campaign appearances would be sensible," Kern said.

Press freedom, 'foreign word'

Kern also slammed Erdogan's plan, saying "the introduction of a presidential system would further weaken the constitutional state, constrain the separation of powers and contradict the values of the European Union."

Press freedom had become a foreign word in Turkey and human rights are being trampled on, Kern added.

He demanded Ankara immediately free the German-Turkish correspondent of the conservative German newspaper "Die Welt," as well as numerous other journalists and scientists detained since last year's coup attempt in Turkey.

Yucel had reported on Turkey in an independent and critical manner, Kern said.

Erdogan: 'German agent'

On Friday, Erdogan accused Yucel of being a "German agent" and supporting the armed Kurdistan Workers' Party (PKK) through his reporting.

Meanwhile, Turkish Prime Mnister Binali Yildirim said he had had a long phone call with German Chancellor Angela Merkel. Her office has yet to comment on the contents of the call.

Merkel did, however, defend the decision of local officials obligated to uphold social freedom.

Those decisions were "taken by municipalities, and as a matter of principle, we apply freedom of expression in Germany," she said.

Stephan Meyer, interior affairs spokesman for Merkel's Bavarian allies, the Christian Social Union (CSU), said the "export" of Turkey's internal conflict to Germany should "not be tolerated." 

Germany's new Foreign Minister Sigmar Gabriel of the center-left Social Democrats, which governs with Merkel, warned against a further escalation of recriminations.

"We should not wreck the foundations of the friendship between our countries," Gabriel wrote in a guest article published by another German Sunday newspaper "Bild am Sonntag."

Opposition Greens party politician Claudia Roth warned that appearance bans would turn out to be counter-productive.

"Then we best demonstrate most clearly the difference between us and an autocracy on its way to dictatorship when we show that freedom of opinion, freedom of assembly and, of course, press freedom applies to all," Roth said.

More than one million Turks living in Germany are eligible to vote in Turkey's referendum in April. They are among three million persons of Turkish origin living in Germany. Half of them have German citizenship.

Netherlands chastised

Turkish Foreign Minister Mevlut Cavusoglu, speaking in Antalya, western Turkey, also chastised the Netherlands after authorities in Rotterdam banned a Turkish rally planned for next week.

On Dutch radio, Deputy Prime Minister Lodewijk Asscher rejected accusations that the Netherlands was restricting free speech.

"We believe that the Dutch public space is not the place to conduct another country's political campaign," Prime Minister Mark Rutte said in a statement on Facebook on Friday.

"We will go where we want to go, we will meet with our citizens and we will have our meetings," said Cavusoglu in response to Rutte's post.

ipj/jlw (Reuters, AFP, dpa)