BEIJING - A top U.S. envoy said Wednesday that Washington could penalize China's four biggest state banks if they were found doing business with an Iranian insurance company in violation of U.S. nuclear sanctions.

David Cohen, Treasury under secretary for terrorism and financial intelligence, was in China to discuss measures to prevent Iran from obtaining financing for its nuclear weapons program and means to spread its hardware.

His China trip followed a stop in Hong Kong, where he met with representatives of the four banks - Bank of China Ltd., China Construction Bank Corp., Industrial and Commercial Bank of China Ltd. and the Agricultural Bank of China.

Speaking to journalists Wednesday, Cohen said he told the banks if they accepted payment from Moallem, an Iranian insurer, they could be cut off from the financial system under a 2010 U.S. law promoting tighter sanctions on Iran.

Moallem insures Iran's national bulk container carrier, the Islamic Republic of Iran Shipping Lines, or IRISL, a company with three subsidiaries, in violation of United Nations Security Council resolutions.

Both Moallem and IRISL have been designated as violators of anti-nuclear proliferation rules set by the United States and the European Union.

Many European countries no longer do business with IRISL and have closed their ports to its ships, but the vessels still make calls in Asia, Cohen said.

In January, the Treasury identified several Hong Kong-based shipping companies as having strong links with IRISL.

Cohen also met with 20 financial institutions, local port authorities and shipping companies in Hong Kong to encourage them not to deal with IRISL or Moallem.

"Any foreign bank that receives payment from Moallem on behalf of a client, risks losing its ability to do business in the United States," he said.

In two days of meetings in Beijing, Cohen met with officials from China's Ministry of Finance, Ministry of Foreign Affairs and ruling Communist Party.

The United States and other world powers accuse Iran of seeking to acquire a nuclear weapons capacity under the guise of its civilian atomic work, a charge Tehran strongly denies.

Iran is under five sets of U.N. Security Council sanctions, as well as U.S. ones, over its nuclear program.

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