British American Tobacco has agreed to pay more than $635 million as a penalty for selling cigarettes to North Korea through an intermediary in Singapore, in violation of American sanctions. A small portion of the amount, about $5 million, was part of a civil settlement with the Treasury Department. The rest, obtained and announced by the Justice Department on Tuesday, was the biggest in that department’s history related to sanctions on North Korea. North Korean clients paid that intermediary, which was not identified in the filing, at least $415 million through front companies over about a decade, in some cases using American banks, according to the court documents. The operation relied on “financial facilitators linked to North Korea’s weapons of mass destruction proliferation network,” Brian E. Nelson, the Treasury’s under secretary for terrorism and financial intelligence, said in the statement issued by the Justice Department.

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