Comments from Turkish President Recep Tayyip Erdogan and other officials accusing Germany of "Nazi practices" cannot be tolerated and need to stop, Chancellor Angela Merkel has told parliament.
In her strongest comments so far about Mr Erdogan's statement, Mrs Merkel said the Nazi comparisons were "sad" and "so incredibly misplaced that one really can't comment, but they cannot be justified".
"We will not allow the victims of the Nazis to be trivialised," she said.
"These comparisons with the Nazis must stop."
Mr Erdogan made the comment on the weekend after several German municipalities cancelled events in which Turkish cabinet ministers had planned to address rallies in Germany in support of a national referendum on constitutional reform that would give the Turkish president more powers.
Officials have cited problems with overcrowding and fire safety, and other issues
About 1.4 million people of Turkish descent living in Germany are eligible to vote in the referendum.
In a step back from the heated rhetoric of recent days, Turkish Prime Minister Binali Yildirim told reporters in Ankara on Thursday that Germany seems to be taking sides in the upcoming referendum, but he did not repeat the Nazi comparison.
Asked about Mrs Merkel's comments, Mr Yildirim said Germany "may be disturbed" that a yes vote is likely in the referendum, but that if it is interfering in the process it amounts to "meddling" in another country's affairs and is "very wrong".
Some rallies have gone ahead, and Mrs Merkel's government has emphasised it was not involved in blocking the others, but must respect the decisions of local authorities.
But as the rhetoric in Ankara has escalated, German officials have been expressing increasing irritation with Turkey.
Adding to the tension has been Turkey's arrest in February of German newspaper reporter Deniz Yucel, whom Mr Erdogan has accused of being both a German spy and a "representative" of the outlawed Kurdish rebel group PKK.
Mr Yucel, a reporter for Die Welt with German and Turkish citizenship, was detained in Istanbul over his reports about a hacker attack on the email account of the country's energy minister.
Germany has dismissed Mr Erdogan's claims about Mr Yucel as "absurd", and Mrs Merkel told parliament that the government is working "with all its means" to secure Mr Yucel's freedom.
She told politicians that in all of her government's talks with Turkey, she and other German officials have emphasised Turkey's need to respect "freedom of opinion, freedom of speech and freedom of the press".
The first face-to-face meeting between German and Turkish officials in the wake of the recent diplomatic friction came on Wednesday when foreign minister Sigmar Gabriel and Turkish foreign minister Mevlut Cavusoglu sat down over breakfast at a Berlin hotel.
Mr Gabriel called the meeting "good, honest and friendly, but also hard and contentious" and the two sides agreed to meet again in Turkey.