BBC News
The US Treasury says Hong Kong Electronics moved millions of dollars to two North Korean companies linked to Pyongyang's nuclear programme.
The action means that bank accounts or any other financial assets found in the US belonging to the Iran-based company will be frozen.
US citizens are also banned from doing business with the firm.
"North Korea uses front companies like Hong Kong Electronics and a range of other deceptive practices to obscure the true nature of its financial dealings," said Stuart Levey, US Treasury under-secretary for terrorism and financial intelligence.
"Today's action is part of our overall effort to prevent North Korea from misusing the international financial system to advance its nuclear and missile programs and to sell dangerous technology around the world," he added.
The US has previously imposed sanctions and financial restrictions on a number of firms linked to Iran and North Korea in an attempt to curb what it sees as efforts to proliferate dangerous weapons.
'Arms dealers'
The US Treasury says Hong Kong Electronics – based on Kish Island, in southern Iran – has since 2007 transferred millions of dollars to North Korea's Tanchon Commercial Bank and the Korea Mining Development Trading Corporation (Komid).
Washington accuses the companies of supporting the spread of weapons of mass destruction and has already acted in the past to financially isolate them.
The US Treasury describes Komid as North Korea's "premier arms dealer" and calls Tanchon its financial arm.
A statement from the treasury also accused Tanchon of having an "active relationship" with various branches of the Iranian bank Sepah, which is under UN sanctions for providing financial services to Iran's missile program.
Washington blacklisted Sepah in 2007, accusing it of having a key role in financing the development of weapons of mass destruction.
The UN has extended sanctions against North Korea following its nuclear test in May, which was followed by a series of missile launches.
