WASHINGTON (AP) - Defense Secretary Leon Panetta says he's seen no outward sign that North Korea will follow through soon on its plan to conduct a third nuclear test.
But he says that doesn't mean much because Pyongyang has the ability to test in ways that are difficult to detect.
Panetta says the U.S. is "very concerned" with North Korea's announcement of a planned nuclear test - which he called "needlessly provocative."
The White House says North Korea's plan to conduct a nuclear test is, quote, "needlessly provocative" and will only increase Pyongyang's isolation.
Spokesman Jay Carney says a test would be a significant violation of U.N. Security Council resolutions.
He told reporters Thursday, quote, "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 Thursday that its long-range rockets are designed not only to launch satellites, but to carry warheads aimed at striking the U.S. 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 Carney said the U.S. would be taking additional steps he did not specify.