North Korean leader Kim Jong Un reacts with Ri Pyong Chol (L), in this undated photo released by North Korea's Korean Central News Agency (KCNA) on May 15, 2017.

The United States on Tuesday sanctioned two top North Korean officials involved in the rogue state's ballistic missile development programs.

The new sanctions follow the adoption on Friday of a United Nations Security Council resolution that imposed harsh new restrictions on the country in response to its Nov. 28 missile test. North Korea called Friday's sanctions an act of war.

"Treasury is targeting leaders of North Korea's ballistic missile programs, as part of our maximum pressure campaign to isolate the DPRK and achieve a fully denuclearized Korean Peninsula," Treasury Secretary Steven Mnuchin said in a statement.

The two individuals sanctioned on Tuesday often appear with North Korea's leader, Kim Jong Un, in photos and videos. An article from Reuters in May called Kim Jong Sik and Ri Pyong Chol, as well as a third, Jang Chang Ha, "clearly Kim's favorites."

The Treasury Department said Tuesday that Kim Jong Sik is reportedly a key figure in North Korea's attempts to switch from liquid to solid fuel, which could allow North Korea to launch missiles with less warning.

Ri is a former air force general who experts have said is key to the country's missile programs.