REUTERS - Indian shares reversed early gains and closed at their lowest in two weeks as investors booked profits a day before U.S. Federal Reserve Chair Janet Yellen's speech that is expected to provide clues on outlook for U.S. interest rates.

Thursday's trading session was volatile on account of monthly derivative contracts expiry.

Firming up as much as 0.38 percent earlier in the day, the broader NSE Nifty slipped in the latter half to close down 0.67 percent at 8,592.20, recording its biggest loss since August 10.

The BSE Sensex fell 0.80 percent to 27,835.91, posting its biggest fall in two weeks.

(Reporting by Aastha Agnihotri in Bengaluru; Editing by Vyas Mohan)