The North said an unspecified number of "traitors" including North Koreans who defected to South Korea were arrested recently for their attempt to destroy statues and monuments.
South Korean intelligence authorities hired the defectors and helped them infiltrate into the North, the committee for the peaceful reunification of fatherland, a state body handling cross-border affairs, said in a statement through state media.
Evidence proved the United States was also involved actively in the plot to hurt the dignity of the North's leadership, it said.
"This is a heinous attack on the dignity of (North Korea's) supreme leadership," the committee said.
More than 23,500 refugees have settled in the South since the 1950-53 Korean War. The North customarily describes defectors to the South as "human scum" who betrayed their country.
North Korea, whose personality cult surrounding its ruling family is like a state religion, has built numerous monuments for its late founding leader Kim Il-Sung who died in 1994 and his son Kim Jong-Il who died last December.
It has also carved messages praising the dynasty on hundreds of rocks and cliffs.
The North unveiled a massive carving 120 metres wide across a natural rock face to mark Kim Jong-Il's birthday in February.
In April, two giant statues of Kim Il-Sung and Kim Jong-Il were unveiled in Pyongyang, just hours after the North's failed rocket launch.
The North has threatened attacks on the South's government and conservative media for perceived insults to its regime during Pyongyang's April commemoration of the centenary of Kim Il-Sung's birth.