The $350 million in question is being held by the European-Iranian Trade Bank which is majority-owned by Iranian state-owned banks, and registered with Germany's central bank.
Authorities in German have started investigating an Iranian government plan to transfer hundreds of millions of euros from Hamburg to Tehran.
Iran wants to fly the money out as soon as possible to avoid the potential freezing of accounts as a result of reimposed US sanctions coming into effect in August, reported local daily, Bild.
German lawmakers have accused the US of improperly exerting pressure on Berlin.
The money would be passed on to Iranians lacking a valid credit card to use while travelling abroad and in need of cash.
Under impending US sanctions, Iranian banks will be excluded from the main credit card networks, including VISA and Mastercard, making it difficult for Iranians travelling outside the country.