North Korea threatened on Friday (January 25) to attack rival South Korea if Seou joined a new round of tightened U.N. sanctions, as Washington unveiled more of its own economic restrictions following Pyongyang's rocket launch last month.

In a third straight day of fiery rhetoric against regional powers, the North directed its verbal onslaught at its neighbor, saying: "'Sanctions' mean a war and a declaration of war against us."

The reclusive North has this week declared a boycott of all dialogue aimed at ending its nuclear program and vowed to conduct more rocket and nuclear tests after the Security Council censured it for a long-range missile launch in December.

North Korea's state-run television KRT carried a message from the government targeting South Korea, quoting North Korea’s Committee for the Peaceful Reunification of Korea.

"If the puppet group of traitors takes a direct part in the U.N. sanctions the DPRK (North Korea) will take strong physical counter-measures against it."

The committee is the North's front for dealings with the South.

Seoul has said it will look at whether there are any further sanctions that it can implement alongside the United States, but said the focus for now was to follow Security Council resolutions.

The resolution said the council "deplores the violations" by North Korea of its previous resolutions, which banned Pyongyang from conducting further ballistic missile and nuclear tests and from importing materials and technology for those programs. It does not impose new sanctions on Pyongyang.

- Reuters