But the sanctions against the North Korean bank, announced in 2009, did not stop Dandong Hongxiang from disguising its business for seven years, the United States alleges. Some of the paperwork that Ms. Ma and her colleagues filed to set up shell companies is in the Panama Papers, the enormous trove of leaked records about offshore companies that was made public this year by the Washington-based International Consortium of Investigative Journalists.

Mossack Fonseca, the Panamanian law firm whose files were leaked, helped set up some of Dandong Hongxiang’s shell companies, and the documents show that at least in one instance, it appeared to do little to comply with rules that even lax offshore jurisdictions set up to help prevent money laundering.

Those documents show that in May 2011, two years after Ms. Ma set up her joint-venture company with the North Korean bank, she registered a shell company in Seychelles, the Indian Ocean island nation that in recent years has become a haven for money laundering because of its corporate secrecy rules.

The dozens of leaked internal emails about the shell company, Sky Bright Development, do not reveal its purpose, but such shells can be used to hold stakes in other companies or to set up bank accounts that are extremely difficult to trace. The registration was facilitated by Mossack Fonseca, which specializes in setting up offshore companies for clients around the world, and whose biggest market is China.

Mossack Fonseca conducted a search to find out whether Ms. Ma had any criminal background or was a “politically exposed person,” or P.E.P. — usually an individual with a government post, or a relative of such a person. Seychelles requires extra scrutiny when such people set up offshore companies, including efforts to verify the source of the company’s funds, because of the possibility that they are doing so to conceal corruption.

In this case, an online search by Mossack Fonseca determined that Ms. Ma was, in fact, a P.E.P., showing in its first result that she was a lawmaker in Liaoning, her home province in China, according to the leaked records. Yet Mossack Fonseca’s own internal records subsequently indicated that she had not been designated a politically exposed person.

Representatives at Mossack Fonseca’s Hong Kong and Seychelles offices did not respond to an email seeking comment, and no one at Dandong Hongxiang answered a phone call made during working hours on Tuesday.