* Citigroup tumbled more than 20 percent to $5.38, a slide that put the S&P index of financial companies <.GSPF> on track for its fourth day of losses, the longest losing streak since Citigroup got government aid in November.

* The Dow Jones industrial average <.DJI>, which fell as much as 2 percent, was down 145.36 points, or 1.69 percent, at 8,453.82 in late trading. The Standard & Poor's 500 Index <.SPX> lost 22.04 points, or 2.48 percent, at 868.31. The Nasdaq Composite Index <.IXIC> shed 35.07 points, or 2.23 percent, at 1,536.52.

(Reporting by Deepa Seetharaman; Editing by James Dalgleish)