A statement released by North Korea's official KCNA news agency on Thursday, cited the general staff of the Korea People's Army which said it had "ratified" an attack against the United States, including the use of nuclear weapons.

The statement said the nuclear threat posed by the US would be "smashed by the strong will of all the united service personnel and people and cutting-edge smaller, lighter and diversified nuclear strike means of the DPRK (North Korea) and the merciless operation of its revolutionary armed forces."

Also on Thursday, South Korea's defense minister told lawmakers in Seoul that North Korea had moved a missile with what he described as "considerable" range to its east coast. However, Kim Kwan-jin rejected reports in the South Korean and Japanese media indicating that it could be a long-range missile capable of hitting targets in the United States. As for the reason for the move, Kim said he could only speculate that it was for the purpose of "testing or drills."

The Yonhap news agency quoted an unnamed South Korean official who said they were "closely monitoring whether the North moved it with a view to actual launch or just as a show of force against the US."

Experts in the field do not believe the North currently has fully functional long-range missiles.

Despite this fact, Washington is taking North Korea's threats seriously.  On Wednesday, the Pentagon announced plans to step up security, particularly for its troops in the Pacific region by sending ground-based missile interceptors to be deployed on the US territory of Guam.

The  Terminal High Altitude Area Defense system (THAAD)  "will strengthen defense capabilities for American citizens in the US territory of Guam and US forces stationed there," the Pentagon statement said.

Speaking at the National Defense University in Washington on Wednesday, Defense Secretary Chuck Hagel said the US continued to work with its allies in Asia to try to reduce tensions between it and South Korea.

"There is a pathway that is responsible, for the North to get on the path to peace, working with their neighbors... but they've got to be a responsible member of the world community," Hagel said.

Meanwhile, for a second consecutive day, North Korea prevented South Koreans from crossing the border to work at the Kaesong Industrial Park, where more than 100 mainly small South Korean firms operate, employing around 50,000 North Koreans.

Pyongyang has allowed South Korean managers to leave the industrial part, located five kilometers (three miles) inside North Korean territory. However, hundreds have chosen to stay, fearing they may not be able to return to run their businesses for the foreseeable future.

In recent days, North Korea has threatened to shut down Kaesong entirely over what it sees as "hostile" joint military exercises carried out by the US and South Korea.

pfd/hc (Reuters, AP, AFP)