Tokyo stocks plunged Monday morning, with the benchmark Nikkei down over 2 percent, tracking a tumble on Wall Street late last week on increased concerns over a potential invasion of Ukraine by Russia. The 225-issue Nikkei Stock Average fell 725.74 points, or 2.62 percent, from Thursday to 26,970.34. Japanese financial markets were closed Friday for a national holiday. The broader Topix index of all First Section issues on the Tokyo Stock Exchange was down 39.61 points, or 2.02 percent, at 1,923.00. Decliners were led by rubber product, precision instrument and electric appliance issues. The U…