South Korea on Wednesday fired 20 machine gun warning shots after a North Korean drone briefly crossed the rivals’ border, South Korean military officials said.It is the first time shots have been fired in what has so far been a Cold War-style standoff between the Koreas in the wake of the North’s nuclear test one week ago.The North Korean drone was flying dozens of meters (yards) south of the border and turned back to the North after the South fired, South Korean defense and military officials said, requesting anonymity because of office rules. The shots didn’t hit the drone. North Korean drone flights across the world’s most heavily armed border are rare but have happened before.North Korea has in recent years touted its drone program, a relatively new addition to its arsenal. In 2013, North Korean leader Kim Jong Un watched a drone attack drill on a simulated South Korean target. -