North Korea on Friday marked the anniversary of its shelling of a South Korean border island with a threat to turn South Korea's presidential office into a "sea of fire".The threat came as the South's army, navy, air force and marine corps launched an intensive military drill on and around Yeonpyeong Island in memory of the incident in which four people were killed in November 2010.
"Three years ago the baptism of retaliatory fire was limited to Yeonpyeong, but next time the presidential Blue House and all headquarters of the puppet regime will be targeted," the North's Korean People's Army said in a statement.