North Korea drone entered no-fly zone near Yoon's office, South saysSEOUL, Jan 5 (Reuters) - A North Korean drone briefly entered a no-fly zone surrounding South Korea's presidential office when it intruded into the South's airspace last week, Seoul's military said on Thursday, fuelling criticism over its air defences.The drone was among five North Korean drones that crossed into the South on Dec. 26, prompting South Korea's military to scramble fighter jets and helicopters."A movement of developing medium- and large-sized drones for long-distance reconnaissance has been detected but it appears to be at an early stage, and securing technologies such as high-performance detection sensors would be key," Yoo said after a briefing by the spy agency.The border crossing has sparked criticism over South Korea's air defences at a time of the North's growing nuclear and missile threats.It also unveiled plans last week to spend 560 billion won ($441 million) over the next five years to boost its anti-drone capability, including developing airborne laser weapons and signal jammers."