EU chiefs on Wednesday blasted Turkey's Nazi comparisons with The Netherlands and Germany as "detached from reality" and incompatible with its ambitions to join the bloc.
The leaders' comments came as Dutch voters went to the polls in a key test of right-wing populist strength ahead of elections in France next month and Germany later this year.
The Dutch vote has been overshadowed by a blazing diplomatic row after the government banned Turkish ministers from addressing a pro-Ankara rally in Rotterdam.
European Union president Donald Tusk said no one could make comparisons between events in Rotterdam and the Nazi period, when the city was "brutally destroyed" by the Germans.
"If anyone sees fascism in Rotterdam, they are completely detached from reality. We all show solidarity with The Netherlands," Tusk told the European Parliament in the French city of Strasbourg.
"The Netherlands is Europe, and today I want to say that Europe is The Netherlands. A place of freedom and democracy."
Tusk repeated the statement in Dutch to applause from MEPs.
European Commission chief Jean-Claude Juncker said he was "scandalised" by the Turkish government's Nazi comments.
"I will never accept this comparison between the Nazis and the (modern-day) governments," Juncker said.
"If you are establishing a comparison with that period this is totally unacceptable. The one who is doing this is taking distance from Europe and not trying to enter Europe," he said.
Turkey resumed long-stalled accession talks with the European Union in 2005 but they have made little progress amid growing criticism of Ankara's human rights record.
Relations became much worse after a failed military coup in July against President Recep Tayyip Erdogan, who embarked on a widespread crackdown in response and is now seeking increased powers in a referendum next month.
EU officials say the mass purges and arrests, running into the tens of thousands, breach the EU rights and democratic norms a candidate member must ensure.
Guy Verhofstadt, leader of the liberal group in the parliament, told MEPs it was "time to freeze accession negotiations with Turkey".
"Europe won't be threatened by a tyrant who imprisons journalists," said Verhofstadt, a former Belgian premier who is also the parliament's chief Brexit negotiator.
Erdogan was being "cynical" in calling The Netherlands fascist when he was "building an authoritarian regime in Turkey," Verhofstadt added.