The DPRK statement said that "settling accounts with the US needs to be done with force, not with words, as it regards jungle law as the rule of its survival".

The US has more than 28,000 troops in the Republic of Korea.

Pyongyang has cited the US troops as a key reason to develop nuclear weapons.

In an earlier response, the DPRK rejected involvement in any future disarmament negotiations. Washington urged Pyongyang on Thursday not to proceed with the nuclear test.

"Whether North Korea tests or not is up to North Korea," Glyn Davies, the top US envoy for DPRK diplomacy, said in Seoul. "We hope they don't do it, we call on them not to do it. It would be a mistake and a missed opportunity if they were to do it," Davies said after a meeting with ROK officials, speaking shortly before Pyongyang's statement. Davies will soon fly to Beijing.

"This is not a moment to increase tensions on the Korean Peninsula," he said.

Seoul on the same day voiced deep regret at the plan. "Our government once again strongly urges North Korea to pay heed to the international community's constant warnings and not commit any further provocative acts including nuclear tests," ROK Foreign Ministry spokesman Cho Tai-young said.

The UN Security Council resolution threatened "significant action" if Pyongyang fulfilled a third nuclear test.

It is widely speculated that the nuclear test of a "higher level", as Pyongyang announced, would use highly enriched uranium instead of plutonium. The DPRK declared in 2009 that it would begin enriching uranium.

Zhang Liangui, a professor on Korean Peninsula studies at the Party School of the Communist Party of China Central Committee, said it's still early for the DPRK to conduct a successful nuclear test. "Usually a successful nuclear test comes after about 10 trials," he said.

And the DPRK has an even longer way to go before it can potentially send nuclear warheads to the US, he added.

As for the time of the test, Zhang said it will likely be on April 15 - Kim Il-sung's 101st birthday. Reuters quoted analysts as saying that the test could also be staged as early as Feb 25 as the ROK's President-elect Park Geun-hye is sworn in.

But Liu Jiangyong, vice-dean of the Institute of Modern International Relations at Tsinghua University, said it is too early to say whether and when the DPRK will conduct nuclear test as it is now "very emotional" after the UN resolution.

Though Washington and Seoul are reportedly discussing the possibility of bilateral sanctions against Pyongyang, aside from the UN resolution, Liu said that will not really work as trade ties are quite weak.

Pyongyang's reaction now is the result of sanctions, and sanctions alone cannot solve the nuclear impasse, he said.

Yu Shaohua, director of the Department for Asia-Pacific Security and Cooperation Studies of the China Institute of International Studies, noted that "Pyongyang's pursuit of a nuclear deterrence is due to deep security concerns. In that regard, relevant parties, including the US and the ROK, are responsible for the situation."

Contact the writers at lixiaokun@chinadaily.com.cn