Updated

A Treasury Department official said Thursday a new U.S. sanctions program is disrupting North Korean and Iranian companies' ability to help their countries develop nuclear weapons.

Robert Werner, director of Treasury's Office of Foreign Assets Control, said U.S. actions help unravel the support networks that allow the development of nuclear weapons.

"We target not only the missile or bomb maker, but the procurement fronts, the brokers and middlemen, the logistical apparatus used to move dangerous weapons to market and the financiers," he told a House subcommittee hearing.

He acknowledged, however, that "we're still learning; it's a very, very complicated area."

North Korea has refused to return to international negotiations aimed to rid the communist-led nation of its nuclear weapons programs until U.S. financial restrictions are lifted. Washington maintains the actions are unrelated to the nuclear issue.

Treasury freezes U.S. bank accounts and other financial assets of foreign companies or people associated with illegal weapons sales. It also prohibits Americans from doing business with those targeted.

In October, Treasury designated eight North Korean companies it said had engaged in financial transactions related to weapons proliferation. In January, the department targeted two Tehran-based companies with alleged ties to Iran's nuclear program.

Werner was asked how North Korea's alleged program to counterfeit U.S. currency had helped the nation develop weapons. He said the North's sophisticated counterfeiting program provides the country crucial financial resources, but he said he didn't have further details.

Werner wouldn't discuss current investigations but said more financial actions were coming.

The sanction program's success, he said, could be judged in part by the decision of other countries to join the United States in freezing the assets of targeted companies. President Bush's latest budget request, Werner said, would add 25 jobs to the 125-member office.