In a pivot from her previous position, the centre-right leader declared on Sunday: "The fact is clear that Turkey should not become a member of the European Union".
German Chancellor Angela Merkel has won the single pre-election televised debate against her opponent Martin Schulz ahead of the national elections on September 24, a poll said. More than half of viewers, 55 percent, named Merkel the victor, according to an ARD poll.
'Apart from this, I'll speak to my colleagues to see if we can reach a joint position on this so that we can end these accession talks, ' Merkel added.
Mrs Merkel made the promise after being challenged by her main rival for chancellor, Martin Schulz.
Germany will also look at imposing "real restrictions on economic contact" with Turkey, as well as possibly issuing a tougher travel warning against travel to the country, she said. "But I think one must say in the clearest terms that for us, there can only be a peaceful diplomatic solution".
A ZDF survey was closer but still had Merkel ahead with 32 percent, against 29 percent who thought Schulz performed better.
Three weeks before the federal election, Merkel and her party lead in all polls, including personal popularity surveys.
Much of the debate was taken up with the issue of migrants, with Merkel saying she stood by her decision to allow hundreds of thousands of refugees into Germany in 2015 and insisted the country can't isolate itself from the effects of wars and poverty elsewhere in the world. Merkel called it a "very dramatic situation" that forced her to make a decision. "There are times in the life of a chancellor when she has to decide".
Schulz said that he agreed with the policy of granting asylum to those in need and argued that Germany had to meet its worldwide commitments.
The decision to open Germany's borders boosted the nationalist Alternative for Germany party, which is expected to enter Parliament for the first time as a result of the September 24 vote.