Turkish President Recep Tayyip Erdogan suggested late Wednesday that he might call a referendum on Turkey's participation in membership talks with the European Union, the state-run Anadolu news agency reported.
He accused the bloc of stalling the process because Turkey is a majority-Muslim country.
Earlier Wednesday, a senior official in Brussels said the European Union will start negotiations on a new chapter in Turkey's membership bid on June 30, as required in a migration deal struck with Ankara.
Turkey has officially been a candidate for EU membership since 1999, but progress has been slow, hampered by years of opposition from France and Germany, as well as geopolitical tensions over Cyprus.
Erdogan raised the possibility of a referendum on the eve of the vote Thursday in Britain on remaining in the EU.
"We could ask, should the talks with the European Union go forward or not," he said.
Disagreements with European governments over this year's migration agreement and visa-free entry for Turks to the EU have exposed the bloc's unreliability, Erdogan said.
"You don't keep your promises," he said. "That's your ugly side. Because Erdogan has unmasked this hateful face, you're cracking up."
Turkey demanded progress on its membership bid in exchange for its help in stemming migrant flows to Europe. The migration agreement struck by the two sides in March foresees a new negotiating chapter being opened before July.
As part of the EU accession process, negotiations have to be conducted on 35 chapters, which each cover a policy area in which Ankara must meet EU standards.
The chapter due to be opened on June 30 covers financial and budgetary provisions, including issues such as financial contributions to the EU's budget, according to the senior EU official, who spoke on condition of anonymity.
It would be the 15th accession chapter to be opened in Turkey's membership negotiations, though the most sensitive topics - justice, security and fundamental rights - have so far been avoided.
Negotiations have been concluded so far on just one chapter for science and research.
The prospect of closer ties between the EU and Turkey has proven contentious, amid concerns about Ankara's human rights record and Erdogan's increasingly authoritarian leadership.