Germany's biggest lenders have shied away from business with Iran after past penalties for breaching American sanctions, but smaller banks have leapt on opportunities afforded by the nuclear deal rejected by U.S President Donald Trump.

German exports to Iran have grown since the nuclear deal was signed in 2015, adding 15.5 percent last year to reach almost 2.6 billion euros ($3.0 billion) after 22-percent growth in 2016 .

Germany's two biggest banks, Deutsche Bank and Commerzbank, avoid Iran entirely after being slapped with harsh fines in 2015 over their dealings there, with Deutsche alone paying $258 million in penalties.

Even that linkage could break if Iran's biggest business bank appears on a U.S. list of barred businesses as it has before.

'Effectively protected'Neither does the Bundesbank (German central bank) believe that much has so far changed for business with Iran.

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