On Tuesday, North Korea announced it had restarted operations at its nuclear bomb fuel production plant.

The secretive state says it is fully ready to use nuclear weapons against the United States "and other hostile forces" at any time if they "persistently seek their reckless hostile policy towards the (North) and behave mischievously."

In state media, the North said its plutonium and highly enriched uranium facilities at the main Nyongbyon nuclear complex had been “rearranged, changed or readjusted and they started normal operation.”

Pyongyang issued a warning on Monday, saying it was ready to launch "satellites" on long-range rockets to mark the celebration next month of the communist party's anniversary. The West considers these "satellites" to be banned long-range missiles.

The director of the North’s National Aerospace Development Administration told Pyongyang’s official Korean Central News Agency that scientists were pushing forward on a final development phase for a new earth observation satellite for weather forecasts.

South Korea responded to the news by saying a rocket launch would be a "serious provocation," a military threat and a violation of U.N. resolutions, Yonhap reported.

The Sourth Korean defense ministry’s spokesman Kim Min-seok said, "South Korea and the United States are jointly watching for all possibilities with regard to North Korea's (potential) long-range missile launch,” according to the news agency. “So far, no particular signs have been seen."