Hundreds of people have gathered in Nuremberg to protest against the Iranian leader ahead of a World Cup match between Iran and Mexico.
Anger has also been directed at the German government
The protesters, who include local Jewish community and Iranian exile groups, denounced Mahmoud Ahmadinejad for casting doubt on the Holocaust.
Iranian Vice-President Mohammed Aliabadi is attending the match.
Demonstrators said their anger was targeted at the Iranian leadership and not the country's football team.
But Iranian football fans have expressed their irritation, saying football and politics should not be mixed.
The BBC's Ray Furlong is at the demonstration which he described as "a sea of blue and white Israeli flags".
Bavaria's Interior Minister Gunther Bechstein described Mr Ahmadinejad as a criminal.
"If he comes to Germany, only his diplomatic immunity will save him from arrest," he told the demonstrators.
Alex Delomann, a German Jew from Cologne said his great-grandparents were shot by the Nazis in Ukraine.
"I'm protesting against the Iranian government because I do not think it's OK if somebody claims that my great-grandparents disappeared just like that," he told the Associated Press news agency.
Earlier, police broke up a small counter-demonstration of supporters of the far-right National Democratic Party who were dressed in Iranian jerseys and holding Iranian flags in support of Mr Ahmadinejad.
One of the biggest fears the Germans have for the World Cup is that the Iranian president will come to Germany to watch his team play, our correspondent says.
The Iranian football team's visit has been dogged by politics
Mr Ahmadinejad has so far sent mixed signals on whether he will attend.
Nuremberg is where the Nazis promulgated their infamous race laws and the head of the German Jewish community has declared that the Iranian president is "a second Hitler".
The secretary-general of Germany's Central Council of Jews turned his attention to the German government for failing to deal in political terms with the visit by Iranian Vice-President Mohammad Aliabadi.
In an interview on German radio, Mr Kramer said it had to be demonstrated in no uncertain terms that people who deny the Holocaust would not be welcome in Germany.