The United States imposed sanctions Tuesday on two North Korean officials who are considered key to their country's development of ballistic missiles.

Kim Jong Sik, a veteran rocket scientist, and Ri Pyong Chol, a former senior air force commander, are often seen on television and in photographs with leader Kim Jong Un, walking down the red carpet or sharing a smoke with him to celebrate a successful missile launch.

The sanctions by the Treasury Department mean that any assets the two men hold in the United States can be seized and that Americans are prohibited from dealing with them. More significantly, banks are prohibited from transactions with them involving U.S. dollars, which includes a considerable number of international transactions.

"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," said Treasury Secretary Steven T. Mnuchin, using the initials for North Korea's official name.

The U.S. sanctions followed new punitive measures imposed Friday on North Korea by the U.N. Security Council, which squeeze oil imports and call for countries to repatriate North Korean guest laborers within two years.

The Trump administration has been increasing pressure on North Korea, both at the United Nations and by getting other countries to downgrade or cut off economic and diplomatic ties with the nation.

Kim Jong Sik is considered the mastermind of North Korea's missile program. Under his supervision, the program has been transformed from a slew of failed rocket launches to the successful testing of intercontinental ballistic missiles that can be armed with nuclear weapons and are capable of reaching the U.S. mainland. He holds North Korea's highest honor, the Order of Kim Jong Il.

Ri is deputy director of the Workers' Party Munitions Industry Department, which oversees the ballistic missile program, which was sanctioned by the State Department in 2010. He was educated in Russia.

Both men are said to have been invited to travel with Kim Jong Un, and are numbered among his confidants. In photographs, they are often shown laughing and joking with him, in stark contrast to the deferential manner displayed by most officials.