During a Sunday televised debate with her Social Democrat (SPD) rival Martin Schulz, the center-right leader shocked the audience with an unexpected pledge to discuss an end to Turkey's EU membership talks with fellow European leaders, if she returned for a fourth term in the upcoming German federal elections.
"The fact is clear that Turkey should not become a member of the EU," Merkel said, adding that she never believed it would happen.
"I'll speak to my [EU] colleagues to see if we can reach a joint position on this so that we can end these accession talks."
Initially, Merkel cautioned against such a move, saying it would be irresponsible to cut ties with Turkey at a time when German citizens are in Turkish detention cells on political charges, but eventually made the promise after being challenged by Schulz.
In response, the Turkish government accused both Merkel and Schultz of indulging in populism.
"It is not a coincidence that our president Erdogan was the main topic of the debate," Erdogan spokesman Ibrahim Kalin wrote on Twitter.
"Germany and Europe's attacks on Turkey/Erdogan, by ignoring essential and urgent problems, are reflections of the narrowing of their horizons."
The remarks come amid tense relations between the two states which have worsened following a crackdown launched by Erdogan on dissent in the aftermath of a failed coup attempt in July of last year that many suspected was staged to consolidate the Turkish leader's increasingly autocratic policies at home and abroad.
Relations deteriorated further this year, after Germany banned Turkish pre-referendum rallies on its soil and Ankara refused to allow lawmakers from Berlin to visit the Incirlik Air Base, where German troops are stationed.
Turkey has been in negotiations to join the EU since 2005, months before Merkel became German chancellor. Merkel has always said that she would respect the decision, although her CDU party has consistently opposed EU Turkish membership.