The Treasury said that in 2007 and 2008, Clearstream held an account in a bank in New York on behalf of the Central Bank of Iran that contained USD 2.8 billion worth of securities, violating US controls on financial dealings with Tehran.
Clearstream further transferred the CBI's interests, an act of custody and related banking services under US jurisdiction which the Treasury said constituted an "apparent violation" of the US Iranian Transactions and Sanctions Regulations.
"Today's action should serve as a clear alert to firms operating in the securities industry that they need to be vigilant with respect to dealings with sanctioned parties," he said in a statement.
The Treasury said Clearstream told OFAC officials in 2008 it would terminate its business with Iranian clients.
But it transferred the CBI's assets to another European bank's newly opened custody account at Clearstream.
"This new custody account allowed the CBI to continue holding its interests in the securities through Clearstream's omnibus account in the United States," the Treasury said.