Volker Treier said German companies' trade with Iran has declined sharply as the United States turns up the economic heat on Tehran.
German exports to Iran were down 50 percent in year-on-year terms in the first quarter, while Iranian exports to Germany dropped some 42 percent, Treier told Germany's dpa news agency on Tuesday.
He further said that, of 120 German companies that were active in Iran, 60 are still in the country.
"The US sanctions affect economic relations like a full embargo because the financial sector is affected."
The Trump administration withdrew last year from the 2015 nuclear deal between Tehran and world powers, and reinstated sanctions.