President Barack Obama has approved new expanded sanctions on North Korea over its nuclear programme, weeks after it launched a long-range rocket.
Pyongyang had refused to stop its nuclear programme and the bill was easily passed last week by the congress.
The sanctions attempt to cut off funds needed by North Korea to develop miniaturised nuclear warheads.
The US and China are also negotiating over a UN Security Council resolution on new sanctions.
North Korea recently fired a long-range rocket, which critics said was a test of banned missile technology.
The BBC reported that the morning after the launch, Mr Obama said: “This is an authoritarian regime. It’s provocative. It has repeatedly violated UN resolutions, tested and produced nuclear weapons, and now, they are trying to perfect their missile launch system.”
It came after the North’s fourth nuclear test in January. Analysts said that Kim Jong-un is looking to appear powerful before his important Seventh Party Congress in May.
“The bill was the first one exclusively targeting North Korea, which was passed in an unusually expeditious fashion. We expect it to provide a platform for the US to take strong and effective measures [against North Korea],” said South Korea’s Foreign Ministry in a statement.
The South has said it would be discussing with the US the deployment of a missile defence system.