Hamburg authorities cited fire safety regulations to provisionally call off a Tuesday event where the Turkish Foreign Minister Mevlut Cavusoglu would address 250 supporters, in a move that could exacerbate tension between the two countries.

Hamburg police on Monday said that "considerable shortcomings in fire protection" issues had led to the cancellation. Earlier, police had rejected reports that they were set to call off the rally - saying there was no basis on a crowd control or public safety basis. They also left the door open for Cavusoglu to hold the demo at another location.

According to local media, the fire brigade had complained that a sprinkler system was missing, the smoke extraction system did not work and there were not enough fire escapes.

Cavusoglu was reportedly trying to secure another venue.

Fourth Erdogan advocate to lose his stage

The cancellation came after three other localities banned Turkish ministers' scheduled appearances. In Cologne on Sunday, however, Economy Minister Nihat Zeybekci's campaign speech went ahead as planned.

The canceled rallies were all part of the international bid to expand President Recep Tayyip Erdogan's powers in a referendum set for April and introduced after Erdogan switched to what used to be a ceremonial position.expand President Recep Tayyip Erdogan's powers in a referendum set for April and introduced after Erdogan switched to what used to be a ceremonial position.About 1.4 million Turks in Germany are eligible to vote in the plebiscite and are therefore the target of campaigning - as is commonplace before Turkish general elections, too.

Merkel: Impossible to issue serious response

Turkish President Tayyip Erdogan likened the multiple cancellations to Nazism

In an escalating dispute over the campaign, Erdogan at the weekend likened the cancellations to "Nazi practices." German Chancellor Angela Merkel brushed aside Erdogan's claims on Monday, saying they were so "out of place" that it wasn't even possible to issue a serious comment in response.

Cavusoglu had also accused Berlin of working to scupper the rallies.

"The hotels, the conference halls are being put under pressure, police are being sent to the owners of these places: it's systematic pressure, a maneuver aimed at erecting systematic barriers," he said on Monday.

Turkey heads to the polls in April to decide whether to scrap the post of Prime Minister and expand Edogan's powers

"The state and the state-run institutions are all implicated. That's unacceptable. As for us, we will take the necessary measures, we have no fear of anyone," said Cavusoglu, who was scheduled to meet his German counterpart Sigmar Gabriel on Wednesday.

The other German authorities had cited capacity problems in hosting the events, which they said were likely to attract large crowds. Politicians in other European countries had called for bans on referendum campaigning.

aw/msh (AFP, dpa, AP)