The largest exchange traded fund tracking the U.S. financial sector lost ground Thursday after Jefferies (NYSE: JEF) shares were halted by circuit breakers following a sharp 20% sell-off.

Financial Select Sector SPDR (NYSEArca: XLF) was down 0.6% in recent action.

Jefferies shares were briefly halted Thursday morning, although it wasn’t immediately clear what triggered the share plunge.

The stock pared the loss after trading resumed and was off 6% for the session. Jefferies in a press release said as of Aug. 31 it had “no meaningful net exposure to European sovereign debt.”

After the stock’s pullback this week, Jefferies executives are trying to calm investor worries that the collapse of MF Global will result in losses at the investment bank, Bloomberg reported Wednesday.

The financial ETF is up 12% over the past month.

Financial Select Sector SPDR