BERLIN (Reuters) - Turkish citizens in Germany can vote in Ankara’s referendum on expanding President Tayyip Erdogan’s powers, the German government said on Wednesday, but Turkish politicians might be barred from campaigning among them.

A "Hayir" campaign poster against the referendum in Turkey on the pavement in Berlin March 13, 2017. Picture taken March 13, 2017. REUTERS/Stefanie Eimermacher

Erdogan’s drive to drum up support among Turks living abroad has deeply strained Ankara’s relations with Berlin and other European capitals concerned about what they see as an increasingly authoritarian tone from Turkey.

He has infuriated Germany and the Netherlands by describing bans on planned rallies by Turkish ministers there as “fascist”. On Tuesday, a large number of Twitter accounts in Europe, the United States and Japan were hijacked and replaced with an anti-Nazi messages in Turkish.

Foreign Ministry spokesman Martin Schaefer said Berlin had approved voting by the estimated 1.4 million Turks living in Germany who are eligible to vote in the April 16 referendum.

But he warned that Turkish politicians could be banned from campaigning if they did not respect local laws, including one that bans malicious disparagement of the German government.

“An entry ban would be a last resort. But we reserve the right to do that,” Peter Altmaier, Chancellor Angela Merkel’s chief of staff, told the Funke Mediengruppe newspapers.

Schaefer also chided Turkey for not giving Bulgarian politicians the same rights to campaign for their general election on Sunday among Bulgarian citizens living in Turkey.

Stephan Mayer, domestic policy spokesman for Merkel’s CDU/CSU conservatives, told broadcaster DLF that Germany continued to back freedom of expression, but there were limits.

“We cannot be indifferent if Turkish politicians on German soil are campaigning for a referendum reform that disempowers parliament, abolishes the post of prime minister and gives the president sweeping powers,” he said. “That’s not in our interest.”

The small western state of Saarland on Tuesday banned such rallies, invoking its right to ban activities that jeopardized the peaceful coexistence of Germans and foreigners.

Altmaier said international law allowed all countries, including Germany, to ban the entry of foreign government officials, although this occurred only rarely.

“It’s never happened in Germany, as far as I know,” he said. “But the fact that Germany has not made full use of its options under international law is no free pass for the future.”

Germany’s mass-circulation Bild newspaper carried a nearly-full-page photograph of Erdogan on Wednesday with a headline that read: “You are no democrat! You are damaging your country! You are not wanted here!”

Finance Minister Wolfgang Schaeuble suggested Berlin could curtail financial aid to Turkey, saying Ankara needed to meet certain conditions, including the release of German-Turkish journalist Deniz Yucel, who was arrested in Ankara last month.

Berlin rejects Turkey’s claim that Yucel was working as a German spy, saying it is “absolutely baseless”.

Voting in Turkey’s referendum is scheduled in 13 consulates and other locations around Germany from March 27 to April 9.

Sevim Dagdelen, a lawmaker from Germany’s Left party, sharply criticized plans to give control of some voting urns for the referendum to clerics from the Turkish-German mosque association Ditib, which is under investigation for possible spying on Ankara’s behalf.

“We have to be certain that at least on German territory a free and fair vote can take place, and that it cannot be manipulated by clerics who are clearly working for the Turkish government,” she said after meeting with visiting lawmakers from the pro-Kurdish opposition Peoples’ Democratic Party (HDP).

Cansel Kiziltepe, another German parliamentarian of Turkish origin, said her Social Democratic party shared those concerns.