Upping its rhetoric, North Korea warned Saturday that its military is ready to attack Seoul's presidential palace unless South Korean President Park Geun-hye apologizes for "treason" and publicly executes officials responsible for what Pyongyang says are plans to attack its leadership.The warning, issued by state media in the name of a unit of the Korean People's Army, is the latest in a barrage of threats against Washington and Seoul over joint military drills now underway that the North sees as a dress rehearsal for invasion. It also came shortly after a North Korean propaganda outlet posted a video depicting a nuclear attack on Washington, D.C.The joint military exercises are held annually, but tensions are particularly high this year because the drills are bigger than ever and come on the heels of North Korea's recent nuclear test and rocket launch. Further angering Pyongyang have been reports in South Korean media that this year's exercises include simulated training for a "decapitation strike" targeting North Korea's top leaders.The warning Saturday said the South Korean presidential palace is within striking range of the North's artillery units, and that if an order to attack is made it is "just a click away."North Korea is believed to have artillery capable of striking Seoul with little or no warning and causing severe damage and casualties in the city of 10 million. A strike on Seoul, however, is highly unlikely, and Pyongyang has previously issued similar threats without following through.There were few signs Saturday of the heightened tensions in Pyongyang, where residents went about their daily routines as usual.Earlier on Saturday, the North Korean propaganda website DPRK Today posted a video depicting a nuclear attack on Washington.The four-minute video, titled "Last Chance," showed a digitally created scene of a missile fired from a submerged vessel in the sea soaring through the clouds, darting back to Earth, and crashing into the streets near Washington's Lincoln Memorial before the explosion wipes out the city."Choose, United States. Whether the country called United States continues to exist in this planet depends on your choice," read a message that flashed on the screen to the background of a burning U.S. Capitol building and American flag. The four-minute video also warned that the North will "not hesitate" to attack the United States with its nuclear weapons if "American imperialists even make the slightest move against us."A similar video got a great deal of attention in 2013, when North Korea also conducted a nuclear test and satellite launch.North Korea has been developing its nuclear weapons and missile capabilities, but is not believed to have perfected either enough to pose a credible threat to major U.S. cities.