SEOUL (AFP) - North Korea threatened Thursday to turn South Koreas presidential palace into a sea of fire in response to any provocation, a day after Seouls military held a big exercise near the border. The land, sea and air drill was staged to mark the first anniversary of a deadly North Korean attack on the Souths border island of Yeonpyeong, which sparked outrage among South Koreans and prompted international alarm. Pyongyang has always justified its bombardment on November 23, 2010 as a response to a South Korean artillery drill on Yeonpyeong, which it said dropped shells into the Norths territorial waters.