North Korea has threatened "merciless pre-emptive" attacks on the South ahead of an annual military drill between Seoul and Washington that starts Monday.South Korea's Joint Chief of Staff said Sunday the drills will go forward as planned and that the military will respond firmly and without hesitation if the North fails to heed Seoul's warnings and engages in any form of provocation.The annual four-day Ulchi Freedom Guardian exercise starts Monday and involves some four hundred-80 public servants.The North has long denounced the drills as a rehearsal for war against Pyongyang, while Seoul insists the drill is defensive in nature.Earlier on Sunday, the reclusive regime even took a swipe at South Korean President Park Geun-hye for proposals for inter-Korean exchanges in culture and science that she made in her Liberation Day speech saying she had sidestepped the major issues for mending North-South relations and reunification.