German Chancellor Angela Merkel has said that "profound differences" have overtaken the many common interests shared by Germany and Turkey, and called for efforts to change that.
In an address to the Bundestag, Germany's lower house of parliament, Merkel said that comments from Turkish President Recep Tayyip Erdogan accusing Berlin of "Nazi practices" cannot be tolerated.
She called the remarks "sad and incredibly misplaced" and "not justifiable."
Merkel vowed to "work for German-Turkish relations, but on the basis of our values and in all clarity."
She highlighted German-Turkish ties such as NATO membership and the fight against terrorism.
Erdogan made the comment last week after several German municipalities canceled events in which Turkish officials had planned rallies in support of a national referendum to enhance Erdogan's powers.About 1.4 million people of Turkish descent living in Germany are eligible to vote in the referendum.
Merkel said that Germany "will not allow the victims of the Nazis to be trivialized" by such comparisons.
Her statement comes a day after German Foreign Minister Sigmar Gabriel told his Turkish counterpart that the two countries must work toward restoring frayed ties, but warned that comparisons to Nazis in any dispute are a "red line that cannot be crossed."
Bilateral relations have also been strained since the recent arrest of German-Turkish journalist Deniz Yucel in Turkey.
Yucel, a correspondent for the German daily Die Welt, was accused by Erdogan of being both a German spy and a "representative" of the outlawed Kurdish rebel group, the PKK -- a claim Germany has dismissed as "absurd." Turkey has not yet allowed any German consular access to him.