Turkish President Recep Tayyip Erdogan slammed the European Union on Thursday for demanding the country narrow its terrorism laws, while a top European official warned Turkey alone would be responsible if it failed to secure visa-free access.
Hanging in the balance, and at risk of unravelling, is the migration deal Turkey and Brussels reached in March, which is meant to stem the flow of refugees and others on the move to Europe.
"Since when are you running Turkey?" Erdogan said in a televised speech, while also accusing the EU of "hypocrisy."
With Erdogan already facing criticism that he is growing increasingly authoritarian, Europe insists Turkey must amend its anti-terror laws so that they are less vague and prone to abuse.
European Commission President Jean-Claude Juncker appeared to take a tough stance, saying Erdogan had to ensure all conditions are met before the bloc grants Turkish citizens visa-free access.
"If Mr Erdogan pursues a strategy that denies Turks the right to visa-free travel to Europe, then he must explain this to the Turkish people. This will be his problem, not mine," Juncker told German radio WDR.
The migration deal was reached between Turkey and the EU in March and since then Ankara has been preventing people smugglers from using its coastline to transport migrants and refugees, including many Syrians, to nearby Greek islands, which are part of the EU.
If the deal unravels, there is concern Turkey would relax its controls and migrants would again begin to travel to Europe.
More than a million arrived in the bloc last year, sparking political debates over taking in such large numbers of people.
The influx has prompted border checks and therefore threatened an end to Europe's cherished passport-free Schengen zone.
German Chancellor Angela Merkel defended the migration deal, admitting that there was a "dependency" on Turkey in keeping migration in check.
Her Foreign Minister Frank-Walter Steinmeier told public broadcaster WDR that while there was no plan to back down from criticizing Turkey when appropriate, the migration deal was crucial.
"We must acknowledge that we have a sustainable interest in stopping this agreement on migration from crashing," he said.
But German opposition parties, echoing human rights groups, voiced criticism of the agreement in a parliamentary debate, with the Left Party's Jan Korte calling it a "dirty deal," while Green politician Claudia Roth decried the use of migrants as a bargaining chip.
Europe's parliament is still set to vote on the visa-free access, with the legislative house's president, Martin Schultz, insisting Ankara meet its obligations before the deal can go ahead.
Turkey is meant to meet 72 criteria, including the narrowing of the definition of an act of terrorism, in order to be applicable for the easing of travel laws.
Erdogan used his speech, the latest in a string of lectures criticizing his opponents at home and abroad, to lash out at Europe over its position in the fight against terrorism, implying some members of the bloc are aiding armed groups.
The president also insisted the country needs a constitutional change to empower his office. Critics of Erdogan accuse him of seeking to tighten his grip on power, a factor also weighing on the migration deal.
Next week, Turkish parliament is set to vote on removing the immunity of legislators, a move widely seen as an attempt to crack down on the pro-Kurdish Peoples' Democratic Party (HDP).
Recent months have seen a sharp uptick in violence in the mostly-Kurdish south-eastern provinces of Turkey.