Dutch citizens have been warned over travel to Turkey as a row between the countries shows no sign of abating.

Turkish attempts to hold rallies in Germany, Austria, Switzerland and the Netherlands have been blocked.

Turkey’s President Recep Tayyip Erdogan vowed retaliation, saying: “Nazism is still widespread in the West.”

German Chancellor Angela Merkel rejected his comments as unacceptable and offered the Netherlands her “full support and solidarity”.

On March 13, the Dutch foreign ministry issued a new travel warning, urging its citizens in Turkey to take care and noting the new “diplomatic tensions”.

The warning to “avoid gatherings and crowded places” came as Turkey’s foreign ministry lodged a formal protest with the Dutch envoy.

Meanwhile, Dutch deputy PM Lodewijk Asscher said that “to be called Nazis by a regime which is walking backwards in regards to human rights is just disgusting”.

The row spilled over into the campaign for March 15 general election in the Netherlands, with PM Mark Rutte defending in a live TV debate his decision to stop Turkish ministers addressing Dutch Turks.

His opponent, Geert Wilders of the far-right, anti-Islam Freedom Party, said the real problem was that Turks waving Turkish flags on a Dutch street had shown where their loyalties lay.

European Union leaders called for calm.

The proposed rallies aimed to encourage a large number of Turks living in Europe to vote Yes in a referendum on April 16 on expanding the president’s powers. The plans were criticized by senior EU officials on March 13.

In Germany, for example, there are more than three million people of Turkish origin, of whom an estimated 1.4 million are eligible to vote in Turkish elections. In effect, the diaspora is Turkey’s fourth-largest electoral district.

Planned rallies in Germany, Austria and the Netherlands were blocked after officials cited security concerns or said the rallies could stoke tensions.

A gathering in France went ahead, however, after officials said it did not pose a threat.

Two Turkish ministers were barred from addressing rallies in Rotterdam, with one of them escorted to the German border.

Police used dogs and water cannon against protesters waving Turkish flags in Rotterdam.

President Erdogan likened the Netherlands to “a banana republic”, demanded international organizations impose sanctions on the Netherlands, and accused countries in the West of “Islamophobia”.

“I have said that I had thought that Nazism was over, but I was wrong,” he said.

He later lashed out at the German chancellor.

“Mrs. Merkel, why are you hiding terrorists in your country? Why are you not doing anything?” he said, in comments quoted by AFP.

“Mrs. Merkel, you are supporting terrorists.”

Turkey has previously accused Germany of harboring Kurdish militants and suspects wanted over the failed coup attempt of July 15, 2016.

Turkey’s EU affairs minister, Omer Celik, said Ankara would retaliate against the Netherlands. He later suggested reconsidering part of a deal with the EU aimed at curbing an influx of migrants, namely Turkey’s efforts to prevent them crossing by land to Greece and Bulgaria.

On March 13, the Dutch charge d’affaires in Ankara was summoned for the third time in three days in protest against the treatment of the minister escorted to Germany and the treatment of protesters in Rotterdam.

Mark Rutte said President Erdogan’s comment that the Dutch were “Nazi remnants” was “unacceptable”, and demanded an apology.

Responding to Turkish calls for sanctions, he said the Netherlands would “never negotiate under threat”.

In a news conference on March 13, Angela Merkel said she had condemned Nazi analogies made by Recep Tayyip Erdogan about Germany the previous week.

“This rejection is also valid for our allies. These comparisons are completely misguided… particularly in the Netherlands that endured so much agony through the National Socialists,” she said.

“That’s why the Netherlands can count on my complete support and solidarity in this.”

Danish PM Lars Lokke Rasmussen said he had postponed a meeting later this month with his Turkish counterpart Binali Yildirim because “with the current Turkish attacks on Holland the meeting cannot be seen separated from that”.