"We will take steps ... to convey the message to North Korea that the path it's on doesn't serve its long-term interests, and is not acceptable to the international community. They'll pay a price for the path that they're on if they don't reverse," Rice said in remarks to NBC television, one of several interviews she gave in reaction to Pyongyang test-firing two short-range missiles Tuesday.
The tough words from Washington came a day after the UN Security Council unanimously condemned North Korea for testing a nuclear bomb Monday, as major powers mulled fresh punitive action and US President Barack Obama pledged support to Pyongyang's neighbors.
"You heard the entire international community yesterday from various capitals and from the security council come out swiftly, forcefully and in unity to condemn" the tests, the US envoy told CNN.
"We agreed yesterday we're going to pursue in the security council a new resolution -- a strong resolution with teeth," Rice said, adding that sanctions "could take very different forms" and might include "economic levers."
And in remarks Tuesday to MSNBC, Rice said that international leaders "are prepared to step up our efforts to inspect and interdict ships carrying what we suspect to be prohibited North Korean cargo."
"There are a number of things that we can do and are prepared to do to make it plain that this is the wrong path for North Korea to continue to pursue and that they will pay a price," she said.
"We are committed to a Korean Peninsula that is free of nuclear weapons," Rice said.
After Monday's emergency meeting at UN headquarters in New York, member states decided to "immediately" begin working on a new Security Council resolution to address the weapons tests, council president Vitaly Churkin of Russia said, declaring "strong opposition and condemnation of the nuclear test" by the body.
The UN Security Council said Monday's nuclear and missile tests violated UN Resolution 1718 adopted in October 2006 after North Korea's first atomic test.
The resolution forbids the reclusive regime from conducting any future nuclear tests or missile launches.