The Nikkei index on the Tokyo stock market closed the morning session down 421.55 points, or 0.66 percent, at 63,333.35 points, amid investor concerns that a stronger yen could hurt exporters. This follows remarks on Monday by Japanese Finance Minister Satsuki Katayama that Japan and the United States would not hesitate to take further action to support the yen. Dealers said the market remains cautious about the possibility of another coordinated intervention by authorities, which could push the yen to levels that severely impact corporate earnings.