A report to Congress on North Korea's military capabilities released Wednesday says the secretive nation uses a worldwide network to facilitate arms sales.
It lists Iran, Syria and Myanmar as a core but dwindling group of recipient countries, but adds that Myanmar has begun distancing itself from North Korea.
Myanmar denies violating UN sanctions that prohibit such weapons purchases.
The US has pressed Myanmar's reformist government to stop buying from North Korea, also previously suspected of supplying Myanmar with missile technology.
Washington is concerned that North Korea's arms trade helps bankroll its nuclear and missile programmes.
In December, the US blacklisted a Myanmar military officer and companies for continued weapons trading with the North.