Germany said Friday it was extending by another half year border controls with Austria, which were reintroduced in several places in the passport-free Schengen zone in response to the migrant influx.
"It is important to say in this context that it is still our aim to return to a Schengen without borders, without border controls," Petermann told reporters.
"Travel without border controls is one of the greatest achievements (of the European Union). But we still see problems with the protection of the EU's external borders and we still have high numbers for illegal secondary migration" between member states.
Since 2015, several countries in the 26-nation Schengen zone have reintroduced border controls due to the largest migrant crisis since World War II -- effectively suspending its principle of open-borders travel.
EU rules say countries in exceptional circumstances can reintroduce border controls for up to two years, in periods of up to six months at a time.
Petermann said more than 7,000 people crossed the German-Austrian border illegally this year until August, of whom nearly 4,000 were turned back.
The decision was ordered by Germany's hardline Interior Minister Horst Seehofer, whose conservative party is facing a tough election in the border state of Bavaria on Sunday.
Seehofer nearly toppled Chancellor Angela Merkel's shaky coalition government over the summer with a threat to unilaterally turn back migrants at the border with Austria. Arrivals there have dropped off steeply since 2015-2016.
The dispute was resolved with a more moderate compromise plan involving bilateral agreements between Germany and EU member states.
Merkel's spokesman said Friday that Seehofer's decision on the border checks had been agreed with the rest of the government.