Turkish President Recep Tayyip Erdogan called the European Union a "crusader alliance" on April 2 and said the bloc has been lying for years on accepting Turkey.
Turks will vote on April 16 on constitutional changes that would eliminate the role of prime minister and allow the president to directly appoint public officials, including government ministers.
Erdogan has frequently bashed the EU during a raucous campaign over the changes, often accusing European politicians of supporting his opponents.
"Do you understand why they have not accepted Turkey into the EU after 54 years? I say it loud and clear: It is in every respect a crusader alliance," he said at a rally in Ankara. "I turned out to be right on about what I have been saying [about the EU] ... They have been lying to us for 14 years, and they keep on lying."
Turkey began negotiating EU accession in 2005, but talks have not gained much ground because of several issues, including the dispute over divided Cyprus and domestic human rights.
Tensions between Turkey and the EU have intensified in recent months.
Officials in several major European cities have banned rallies by senior Turkish politicians to promote the constitutional referendum among members of Turkey's European diaspora.
The cancelations led Turkey's president to accuse authorities in Germany and the Netherlands of "Nazi practices" -- language that was sharply rebuked by EU leaders.
Erdogan says the constitutional changes are necessary to protect the country’s stability and would be similar to systems in the United States and France but critics, including many Western governments, say it would put too much power into one person’s hands and eliminate government checks and balances.