The US treasury named the two men as Kim Jong-sik and Ri Pyong-chol, and said both were “key leaders” of North Korea’s ballistic missile programme.
The UN Security Council imposed new sanctions on North Korea on Friday in response to ballistic missile tests.
North Korea said the move was “an act of war” and tantamount to a total economic blockade.
The new US sanctions will block any transactions by the two men carried out in the US, essentially freezing any American assets they may have.
Both men are regularly photographed alongside North Korean leader Kim Jong-un at missile launches.
In the past year, the country has tested ever more ambitious types of missile, and says it can now reach the entire continental United States.
A Reuters investigation in May said that the two men, along with weapons developer Jang Chan-ha, were handpicked by Kim Jong-un and were very popular with him.
Their behaviour around him, Reuters said, “is sharply at variance with the obsequiousness of other senior aides, most of whom bow and hold their hands over their mouths when speaking to the young leader”.
The news agency reported that Ri Pyong-chol was a former air force general educated in Russia and that Kim Jong-sik was a veteran rocket scientist.
They were both among 16 North Koreans placed under UN sanctions on Friday. (Courtesy BBC)