South Korean authorities have tightened security around nine conservative media outlets in Seoul, after North Korea threatened to carry a “special military action” on them by “unprecedented means and methods.”

The government in Seoul says it is concerned about the threat made by Pyongyang Monday to “reduce to ashes in several minutes” the support base for conservative President Lee Myung-bak, including several broadcasters and a leading daily newspaper .

Foreign Ministry spokesman Cho Byung-je said the North's latest threat is “very dangerous and harsh.”

Cho says South Korea's government and military are strengthening their security posture and are on alert to prepare for any situation. He also warns that any military provocation by Pyongyang will be answered with a punishment by the South.

Defense Ministry spokesman Kim Min-suk told reporters Tuesday South Korean forces are monitoring the North's military. He did not elaborate.

Meanwhile, South Korean protesters gathered in Seoul and burnt an effigy of North Korean leader Kim Jong Un. They also urged their northern neighbors to “rise and claim freedom.”

Government officials say there are no reports of any unusual military movements in the North, which could suggest that Pyongyang's threat of the unique assault could be non-traditional, such as cyberattacks on the government and media.

Pyongyang has a long history of terrorist attacks against the South, including attempts to assassinate President Lee.

North Korean state media reported recently that protesters demanded Mr. Lee's killing. Pyongyang has accused the South Korean leader of insulting the country twice — while it was mourning the death of president Kim Jong Il in December and again earlier this month, while celebrating the 100th anniversary of the birth of the nation's founder, Kim Il Sung.