Iranian banks illegally shifted billions of dollars through American financial institutions in recent years, and authorities suspect some of the money may have been used to finance Iran’s nuclear and missile programs.

Details of the illicit transfers came to light on Friday when New York State and federal authorities announced that a large British bank had agreed to pay $350 million to settle accusations that it had helped the Iranian banks hide the transactions.

The British bank, the Lloyds TSB Group, “stripped” information that would have identified the transfers in order to deceive American financial institutions, which are barred from doing business with Iranian banks, Robert M. Morgenthau, the Manhattan district attorney, said. Lloyds acknowledged its conduct and agreed to turn over detailed records of the transactions.

“They went to great lengths to obliterate any identification,” Mr. Morgenthau said.

The district attorney’s office was still investigating nine major banks that might be engaging in similar conduct, but prosecutors declined to name them. Mr. Morgenthau said, however, that money in one transaction was used to buy a large amount of tungsten, an ingredient for making long-range missiles. He said he suspected that other funds might have been used to finance Iran’s nuclear program.