German Chancellor Angela Merkel demanded on Monday that Muslims living in Germany conform to "fundamental German values", saying there was no leeway on the issue.
She spoke a day after Germany's largely ceremonial president, Christian Wulff, had reached out to Muslims in a speech marking 20 years of reunification, assuring them they belonged.
Wulff's remarks were welcomed by one of the country's main Islamic groups, the Central Council of Muslims.
The Christian Democrat chancellor, in remarks promoting a fiercely conservative book by one of her supporters, said Muslims in Germany must orient themselves without reservation to Germany's fundamental values and constitution.
"There is no leeway on this," she said, adding that Germans' perceptions of Islam were dominated by Sharia (Islamic law), the lack of equality between men and women and honour killings.
The book by Roland Koch, a former premier of the state of Hesse who retired this year to go into business, is titled "Conservative. No State Can Be Built Without Values and Principles".
Germany had freedom of religion, and Islam was welcome, "but it must be a form of Islam that feels devoted to our fundamental values", Merkel said. If it were not, fears would develop among Germans, "and that is hardly something we want to happen".
Merkel also criticised talks that have been under way for years between the federal interior ministry and leading Muslim groups in which both sides have tried to articulate concerns about the other.
The results had been "unsatisfactory", said Merkel, adding, "extra work will have to be done". She said she wanted German Muslim children to be taught their faith in public schools and she wanted imams at German mosques who spoke German.
President Wulff had spoken more embracingly the previous day, saying, "Christianity belongs in Germany. Judaism belongs in Germany. And by now, Islam also belongs in Germany."
It was in Germany's national interest to prevent prejudice from festering and people being excluded, he said.
In remarks to the mass-circulation newspaper Bild, the Central Council of Muslims responded, "Wulff's speech was a sign that Muslims are not second-class citizens."
The speech was a "clear, unambiguous and important signal to Muslims living in Germany", Council president Aiman Mazyek said, adding, "Different conceptions of one's life and diversity are being welcomed."