The Treasury Department added the Korea Daesong Bank and Korea Daesong General Trading Corporation to its financial blacklist. The move freezes any assets the companies may have in U.S. jurisdictions and bans Americans from doing business with them.

Treasury said both are part of "Office 39," a secretive bureau that raises money for senior North Korean leaders by producing, smuggling and distributing narcotics, and laundering money. It is also accused of importing luxury goods for top North Korean leader Kim Jong Il, his family, associates and other elite.

These are "key components of Office 39's financial network supporting North Korea's illicit and dangerous activities," Under Secretary for Terrorism and Financial Intelligence Stuart Levey said in a statement.

Thursday's step follows the administration's decision in late August to add Office 39 itself to the blacklist. On Aug. 30, Treasury said that the office was involved last year in a failed attempt to buy, through China, two Italian-made luxury yachts worth more than $15 million for use by Kim.

And, in a report earlier this year, the U.S. Army War College's Strategic Studies Institute said Office 39 is involved in the manufacture and distribution of illegal drugs, the counterfeiting of U.S. currency, and the manufacture and distribution of counterfeit cigarettes.

The sanctions are aimed at pressuring North Korea to return to six-nation nuclear disarmament talks that it quit last year. They are also intended to dissuade the country from taking provocative actions against its neighbors, notably South Korea and Japan after the March sinking of a South Korean warship that killed 46 sailors.