President Barack Obama has signed legislation imposing new sanctions against North Korea for refusing to stop its nuclear weapons program.
The expanded sanctions are designed to deny North Korea the money it needs to develop miniaturised nuclear warheads and the long-range missiles needed to deliver them.
The measure also authorises $50 million US dollars over five years to transmit radio broadcasts into North Korea and support humanitarian assistance programs.
The sanctions from Congress come as the US and China are in delicate negotiations over a UN Security Council resolution on new sanctions.
China has raised concerns about measures that could devastate North Korea's economy.