North Korea has announced it will carry out more rocket launches and a nuclear test.
Quoted by the state news agency KCNA, North Korea's National Defense Commission said such action "will target our sworn enemy, the United States."
The announcement on January 24 by the country's top military body comes a day after the United Nations Security Council passed a resolution to censure and sanction the country for a rocket launch in December.
North Korea said the launch was a peaceful satellite mission, but the United States and others say it was actually a test of long-range missile technology.
The North was banned from developing missile and nuclear technology under UN resolutions imposed after Pyongyang's 2006 and 2009 nuclear tests.
South Korean Foreign Ministry spokesman Cho Tai-young urged the North to reconsider its announcement.
"It is very regrettable that North Korea released such a statement," Cho said.
"Once again, our government strongly urges the North to listen to warnings from the international community and not to carry out additional provocations such as a nuclear test."
The United States' special envoy for North Korea, Glyn Davies, said a nuclear test by North Korea would undermine stability on the Korean Peninsula.
"We hope they don't [carry out further tests], we call on them not to do it. It would be highly provocative," Davies said.
"It would set back the course of trying to find a solution to these long-standing problems that have prevented the peninsula from becoming reunited. I think it's very important that they don't test."
Chinese Foreign Ministry spokesman Hong Lei called on "all relevant parties [to] refrain from action that might escalate the situation in the region."
With reporting by AP, Reuters, and dpa