The Treasury Department on Tuesday imposed economic penalties on six people and three companies accused of helping Iran's government obtain hundreds of millions in U.S. currency or evade existing sanctions.

The action shows that the Obama administration is serious about enforcing sanctions already on the books even though it does not support additional sanctions while the U.S. and its partners work to negotiate with Iran over its nuclear program, said David Cohen, undersecretary for terrorism and financial intelligence.

Obama has threatened to veto any new sanctions legislation while American diplomats continue their push for an accord that would set multiyear limits on Iran's nuclear progress in exchange for an easing of the international sanctions that have crippled the Iranian economy. Senate hawks are still trying to build a veto-proof majority of 67 votes with Republicans set to assume the majority next month.

Those accused of helping Iran convert various currencies into hundreds of millions of U.S. dollars include Iranians, citizens of Afghanistan and St. Kitts and Nevis and a Dubai-based trading company. Iran's Douran Software Technologies is targeted for helping government censorship activities. Another tech firm, Abyssec, is blamed for supporting Iran's Revolutionary Guard corps in cyber tradecraft.

Americans can't do business with those blacklisted. Any assets they have in the U.S. are now frozen.