North Korea is prepared to conduct a nuclear test and carry out more long-range rocket launches, the Pyongyang government has warned.
In a statement carried by state media, the National Defence Commission threatened to wage a "full-fledged confrontation" against the United States for what it calls continued hostility.
The declaration follows the UN Security Council's condemnation of North Korea on Tuesday and expanded sanctions against the regime for launching a rocket in December.
North Korea said the launch was a peaceful satellite mission, but the US and others claim it was actually a test of long-range missile technology.
The White House says North Korea's plan to conduct a nuclear test is, "needlessly provocative" and will only increase Pyongyang's isolation.
Spokesman Jay Carney says a test would be a significant violation of UN Security Council resolutions.
He told reporters: "We judge North Korea by its actions, and provocations like these are significant violations, and we act accordingly."
North Korea also made clear for the first time that its long-range rockets are designed not only to launch satellites, but to carry warheads aimed at striking the US. Its announcement came two days after the Security Council condemned a December satellite launch.
The council further tightened sanctions to impede the North's weapons programs, and Mr Carney said the US would be taking additional steps he did not specify.