Germany, the Netherlands and Austria are committing "crimes against humanity," a top Turkish minister said Friday, further stoking a row between Turkey and Europe over Ankara's attempts to take its referendum campaign to the continent.

"Suporting terrorism and supporting terrorists has no other meaning," said Nurettin Canikli, a deputy prime minister, in televised remarks. He accused Germany of aiding the armed Kurdistan Workers' Party (PKK), including through financial means.

"Europe supports murderous terrorist organizations," Canikli said. "Today, Europe is no longer a region of freedom." He also repeated Turkish government allegations that "Nazi practices" were re-emerging.

He did not provide any proof for his allegations.

Some German towns have called off recent rallies by Turkish ministers ahead of Turkey's upcoming referendum, thwarting the politicians' attempts to court expatriate voters in order to push through proposed constitutional changes.

On April 16, Turks are set to vote on whether Turkey should introduce a presidential system, which would vastly empower the office of Recep Tayyip Erdogan. Critics say the amendments would weaken parliamentary checks and balances.

Dutch politicians have also voiced opposition to planned Turkish government rallies in their country, while Austria is drafting a legal amendment to ban foreign electioneering on its soil.

Despite the opposition, Turkey is pressing ahead with events planned for the weekend.

On Friday, the minister for youth and sport, Akif Cagatay Kilic, is set to appear at various locations in the German city of Cologne, local police said.

Cologne was also the location of a rally attended by Economy Minister Nihat Zeybekci last weekend, after two other events at which he was due to speak were cancelled.

Meanwhile, the Dutch government has informed Ankara that Foreign Minister Mevlut Cavusoglu is not welcome at a visit planned for Saturday in Rotterdam. It is unclear whether he will attend nonetheless.