North Korea is threatening to attack if the U.S. and South Korea go ahead with joint military drills later this month.
An army spokesman warned in a statement carried in official media Thursday that North Korean troops are prepared to "mercilessly destroy" its foes and could even use nuclear means.
The warning comes hours after President Obama's special envoy to North Korea arrived in Seoul from Beijing to discuss how to restart nuclear disarmament talks.
The joint U.S.-South Korean military exercises begin on March 8.
Everyone involved in the diplomatic efforts to resume talks on ending North Korea's nuclear weapons program thinks it's important to return to the talks "as fast as we can," the U.S. special envoy to North Korea said Wednesday.
Stephen Bosworth spoke with reporters after meeting with Chinese nuclear envoy Wu Dawei for what he described as a "very useful exchange of views" on efforts to bring North Korea back to the negotiating table.
Bosworth would not give details of their talk, calling it "premature" to go into specifics.
"I think everybody shares the view that it's important to get back to the negotiating table as fast as we can," he said. The China-hosted talks also include Japan, Russia and North and South Korea.
North Korea last year quit the disarmament-for-aid negotiations and conducted a second nuclear test, drawing tightened U.N. sanctions. The North has demanded a lifting of the sanctions and peace talks formally ending the 1950-53 Korean War before it returns to the negotiating table.
South Korean envoy Wi Sung-lac, who was scheduled to meet with Bosworth on Thursday in Seoul, said the North appears to remain firm in its demands, the Yonhap news agency reported.
"It remains to be seen when the (nuclear) talks will resume," Wi told reporters Wednesday after returning home from Beijing, where he met with China's Wu.
However, the reclusive communist regime sent its nuclear negotiator to Beijing earlier this month for dayslong talks on restarting the negotiations.
North Korea relies heavily on China as its main source of economic aid and diplomatic support.
Chinese President Hu Jintao met Tuesday with Kim Yong Il, the head of a North Korean delegation in Beijing for talks with Chinese officials. The official Xinhua News Agency did not indicate whether the two discussed nuclear talks, but Hu was quoted as saying that it was important to "promote friendly exchanges and expand pragmatic cooperation between the two countries."
Bosworth also will visit Tokyo on Friday.