SEOUL (Reuters) -North Korea fired 10 artillery shells off its west coast on Monday, the North’s official KCNA said, in response to South Korea’s warning shots fired at a North Korean boat that crossed the two Koreas’ maritime border. North Korea fired 10 shells of multiple rocket launchers at around 5:15 a.m. (-1day 2015 GMT) after the South Korean military fired warning shots at around 3:50 a.m. citing patrol activities, a spokesman for the General Staff of the North’s Korean People’s Army said. The South’s Joint Chiefs of Staff said it sent back a North Korean merchant vessel that crossed t…