Police in the German city of Cologne said Sunday they were boosting security around a campaign appearance by Turkey's economy minister, although there were no reported demonstrations planned.
Nihat Zeybekci is slated to speak at a private event in a central Cologne hotel on Sunday evening, after local authorities blocked two public rallies he had planned to woo Turkish expatriate voters for an April 16 referendum.
A police spokesman told AFP a police unit around 100 strong would be on hand if needed, but would not confirm details of the time or location of the event.
With roughly three million people of Turkish origin living in Germany, the country represents the biggest reserve of expatriate voters worldwide for President Recep Tayyip Erdogan as he seeks public approval of constitutional changes extending his powers.
But several German towns have cancelled public campaign events by Turkish ministers in recent days over safety and security concerns, fraying relations between Berlin and Ankara.
While Chancellor Angela Merkel has said it is up to local authorities whether to permit rallies, Turkish Justice Minister Bekir Bozdag on Saturday complained that German leaders "do not say the decision taken by the authorities is wrong."
The justice minister had himself been scheduled to speak in the small western German town of Gaggenau on Thursday, but his rally was also cancelled.
German politicians and commentators have criticised Erdogan's proposed reforms as undemocratic, and Berlin was riled last week by Turkey's arrest of Die Welt newspaper correspondent Deniz Yucel on terrorism charges.