Hwang Pyong So, vice chairman of the Norths powerful National Defence Commission headed by Kim, was one of several officials added to a list of Specially Designated Nationals by the U.S. Treasurys Office of Foreign Assets Control.
Hwang, who holds the rank of Vice-Marshal in the North Korean army, heads its General Political Bureau, often seen as the most powerful position in the military after Kim, who is the supreme commander.
North Korea faces tough new sanctions for its nuclear weapons programme under the resolution passed unanimously by the Security Council on Wednesday, drafted by the United States and backed by the Norths main ally China.
The U.S. Treasury added Hwang to its list along with 16 individuals who are now subject to a travel ban and asset freeze. The measures are also designed to block U.S. nationals from dealing with them.
It also added O Kuk Ryol, one of a geriatric trio said to be behind North Koreas nuclear weapons programme, Reuters reported.
Hwang, who is in his mid-60s, is a close confidant of Kim Jong Un and has had an unprecedented rise to the top rungs of North Koreas leadership in the space of a few years.
He was associated with Kim in the late 2000s when the young man was first named in state media reports announcing his party and military credentials.
He was in the Organisation and Guidance Department (OGD), a powerful and secretive body that finalises appointments within North Koreas leading circles and rose to be its second-in-command, according to South Koreas unification ministry.