Beijing urged restraint on Thursday after Pyongyang said it is planning a third "higher level" nuclear test and more rocket launches aimed at the US.
Washington said the nuclear test, if staged, would be "a mistake and a missed opportunity" for Pyongyang.
Experts said the planned nuclear test is likely to use highly enriched uranium instead of the plutonium used in Pyongyang's previous tests. The test date will probably be Feb 16, the birthday of Kim Jong-il, or April 15, the birthday of Kim Il-sung.
"All parties should refrain from action that might escalate the situation in the region," Foreign Ministry spokesman Hong Lei told reporters in Beijing.
China called for the resumption of the Six-Party Talks, which have been stalled since 2009.
"Currently, the situation on the Korean Peninsula is very complicated and sensitive," Hong said.
The comments came several hours after Pyongyang's top military body, the National Defense Commission, announced a third nuclear test would be conducted, without giving a date.
"We do not hide that a variety of satellites and long-range rockets that will be launched by the DPRK, one after the other, and a nuclear test of a higher level that will be carried out by it in the upcoming all-out action - a new phase of the anti-US struggle that has lasted century after century - are targeted against the US, the sworn enemy of the Korean people," the commission said in a statement, according to state news agency KCNA.
The statement was the latest response from Pyongyang to a United Nations Security Council resolution on Tuesday condemning the December rocket launch by the Democratic People's Republic of Korea. The resolution also expanded existing UN sanctions.
Pyongyang's previous nuclear tests in 2006 and 2009 were carried out within months of long-range rocket launches.
Seoul-based Yonhap News Agency, citing an ROK intelligence source, reported earlier that Pyongyang had finished technical preparations and could conduct a test within days.
A US think tank said last month that, based on satellite photos, the DPRK had repaired damage at its nuclear test site and could conduct a detonation within weeks.
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