The Nikkei stock index plunged over 3 percent Friday morning on selling spurred by concerns over escalating conflict in the Middle East. The 225-issue Nikkei Stock Average fell 1,260.89 points, or 3.31 percent, from Thursday to 36,818.81. The broader Topix index was down 74.38 points, or 2.78 percent, at 2,603.07.