ZURICH (Reuters) – A U.S. anti-terrorism official warned Swiss banks not to do business with Iran on Saturday, saying Iranian officials sought to conceal their identity in deals designed to fund Iran’s uranium enrichment program.

Stuart Levey, the U.S. Treasury’s top anti-terrorism official, said he came to Switzerland as part of a European tour to warn banks that they risked tarnishing their reputations if they did business with Iran, OPEC’s second-largest oil producer.

“We delivered new evidence that implicates Iranian financial institutions in the uranium enrichment program,” Levey said in an interview in French-language daily Le Temps.

“We came to offer new information to Swiss bank executives to make them aware of the risks to their reputation they could run by maintaining financial relations with Iran.”

Washington is leading efforts to isolate the Islamic Republic over its atomic program and has slapped sanctions on two Iranian banks. United Nations sanctions have targeted one bank. Iran denies U.S. claims it aims to build the bomb.

U.S. officials have worked hard behind the scenes to ensure that Iran cannot raise the cash it needs to finance key oil projects as well.

Switzerland’s largest bank, UBS AG, said last year it would cut all ties to Iran, an rare move in a country that has long proven a safe harbor for international deposits.

Rival Credit Suisse said it would not accept any new business but would not sever old ties.

Levey said banks in Switzerland — the world’s largest haven for foreign cash and proud of its tradition of banking secrecy — had been cooperating well with U.S. efforts but that Iranian parties were seeking to conceal their identities.

“Cooperation is good but it takes a continuous effort to prevent development of the Iranian financial system, which is attempting by any means possible to remove the names of the people who are conducting transactions,” he told the paper.