China's official Xinhua News Agency quoted North Korea's official Korean Central News Agency as saying the Communist country would "conduct more nuclear tests, rocket launches."
Separately, South Korea's Yonhap News carried a KCNA item quoting the North's National Defense Commission as saying in a statement its future rocket and nuclear tests may directly target the United States.
KCNA quoted the commission as saying: "In the new phase of our century-long struggle against the United States, we do not hide the fact that various satellites, long-range missiles that we will continue to launch and high-level nuclear test we will conduct will target our sworn enemy, the United States."
Yonhap, citing a South Korean intelligence source, said North Korea has completed all technical preparations for a nuclear test, which would be its third after similar tests in 2006 and 2009. The source said the country needs only a few days' notice to carry it out once the country's leadership makes a decision.
North Korea has been bitterly attacking the latest U.N. Security Council resolution, which was approved unanimously by its 15 members Tuesday, to tighten and expand existing sanctions against it for its Dec. 12 rocket launch. Those sanctions were imposed after North Korea conducted missile tests followed by its two nuclear tests in 2006 and 2009.
The North has maintained its Dec. 12 rocket launch was to place a satellite in orbit, but the United Nations condemned it as a violation of its sanctions and other countries said it was a cover to test the North's intercontinental ballistic missile capability.
Just after the U.N. action, the North pledged to strengthen its "nuclear deterrence" and also to end all efforts to denuclearize under the six-party talks that have not resumed since April 2009 after the North walked out.
In the pledge, the North Korea Foreign Ministry blamed the United States' "worsening policy of hostility" toward North Korea and said the six-party talks on the North's denuclearization, which began in 2005, "were rendered null and the denuclearization of the Korean Peninsula was put to an end."
"There will be no more discussion over denuclearization of the Korean Peninsula in the future although there will be talks for securing peace and security in the peninsula," the ministry said. The six nations in the talks are the two Koreas, China, Japan, Russia and the United States.
Since the Dec. 12 launch, there have been reports North Korea, under its new leader, Kim Jong Un, may be preparing for its third nuclear test.
Glyn Davies, the special U.S. envoy on North Korea policy who arrived in Seoul for talks with South Korea, Thursday warned North Korea against conducting any nuclear test when asked about that likelihood by reporters, Yonhap said.
"Whether North Korea tests or not, it's up to North Korea. We hope they don't do it, we call on them not to do it. It will be a mistake and a missed opportunity if they were to do it," the envoy was quoted as saying.
"This is not a moment to increase tensions on the Korean Peninsula. This is the opportunity (for North Korea) to seize the moment" to engage with the outside world, Davies said.
South Korean officials said Davies and his South Korean counterpart, Lim Sung-nam, discussed additional measures against North Korea in addition to Tuesday's U.N. action, Yonhap reported, but no details were available. The agency had earlier quoted a South Koran diplomatic source as saying the two countries may discuss imposing their own bilateral sanctions against the North.
Yonhap quoted Seoul officials as saying North Korea may test a nuclear device with highly enriched uranium, as that would be difficult to detect immediately. The officials said North Korea currently only has limited amounts of plutonium but has the capacity to produce 40 kilograms of highly enriched uranium per year, enough to make two nuclear devices a year.