The EU-Turkey deal that has substantially reduced the flow of migrants to Europe "must be respected and will be", said European Commission chief Jean-Claude Juncker in an interview published Saturday.
Turkish President Recep Tayyip Erdogan threatened Friday to walk away from the agreement, speaking a day after the European Parliament angered Ankara by backing a freeze of its EU accession talks.
"We made an agreement, it must be respected and it will be," Juncker told Belgium's La Libre Belgique newspaper.
He pointed to the period from 2003-2014 while Erdogan was prime minister, when Turkey "made a lot of progress in terms of the quality of its democracy". But in the past two years, the country has "distanced itself from European principles and values," Juncker said.
"I believe that Erdogan and his government are in the process of 'pre-blaming' Europe for the failure of its accession negotiations," he added.
He noted that the current impasse between the two sides stems in particular from the fact that Turkey has refused to launch a reform of its anti-terror legislation, a condition for membership laid down by the EU.
"Instead of putting this failure on the European Union and Commission, Mr Erdogan would do well to start by asking himself if he responsible for Turks not being able to freely move on European territory," Juncker said.
On March 18, Ankara and Brussels forged a deal for Turkey to halt the flow of migrants to Europe -- an accord that has largely been successful in reducing numbers crossing the Aegean Sea between Turkey and Greece.
According to the International Organization for Migration (IOM), just over 171,000 have crossed to Greece so far this year, much lower than the comparable figure for 2015 of almost 740,000.
Hundreds of migrants drowned while trying to cross the Aegean in 2015 on unseaworthy boats, including three-year-old Syrian Aylan Kurdi. The images of his lifeless body washed up on a Turkish beach spurred the international community into action.
Juncker pointed out that the leaders of the 28 EU nations have the final say on Turkey's bid to join the bloc and not the European Parliament.
Still, he said Thursday's vote was a "warning sign that Turkey should not underestimate".