By Joori Roh SEOUL (Reuters) -North Korea fired two ballistic missiles off its east coast on Thursday, South Korea’s military said, following the firing of two short-range ballistic missiles a day earlier and one on Sunday. “South Korean military detected two short-range ballistic missiles fired from Sunchon, South Pyongan province, toward the east coast between 8:48 p.m. and 8:57 p.m. … Amid strengthened surveillance and vigilance, our military maintains full preparedness while working closely with the U.S.,” the Joint Chiefs of Staff said. The launch came as U.S. Vice President Kamala Harr…