An attorney for Halkbank argued Friday that the Turkish state-owned bank was immune from prosecution in a criminal case alleging that it had helped Iran evade more than $20 billion in U.S. economic sanctions.

The argument came as Halkbank’s defense team is seeking to dismiss a six-count indictment in the Southern District of New York, which charged the bank with conspiracy, bank fraud and money laundering for allegedly moving Iranian oil-and-gas proceeds through the American financial system, in violation of the U.S. sanctions regime.