Austria's president has reminded citizens that their country was a supporter of Nazi Germany and has urged them to be vigilant against a resurgence of extreme-right sentiment.

Heinz Fischer was speaking on the 70th anniversary of the founding of post-war Austria, at a ceremony attended by German President Joachim Gauck and other dignitaries.

Fischer urged Austrians on Monday to "resist the beginnings" of any of the sentiments that led to their country's embrace of Hitler.

Austria long portrayed itself as a victim of Nazi Germany, which annexed the country in 1938. But politicians have since owned up to its role as a major perpetrator of Nazi atrocities.

Fischer said that while many Austrians were opposed to the Nazis or were Nazi victims, "a depressingly large number were sympathizers (and) supporters."