* TSX falls 64.57 points, or 0.51 percent, to 12,672.35 * All of the 10 main index sectors decline * Canadian Natural has biggest negative influence on index By John Tilak TORONTO, Aug 19 (Reuters) - Canada's main stock index fell on Monday, led lower by declines in financial and energy shares as concerns about when the U.S. Federal Reserve will begin exiting its stimulus program hurt sentiment. Every major sector of the benchmark Toronto index was in the red after the index gained the previous week, nearing a three-month high. Rising expectations that the wind-down of the Fed's bond buying program is imminent created more uncertainty in the market, with investors hoping the release on Wednesday of minutes from the Fed's last policy meeting would shed light on the U.S. central bank's intentions. "It looks like we're into shaky waters," said Victor Kuntzevitsky, an associate at Northland Wealth Management. "I do expect more volatility," he added. "Because of the overhang, investors are not sure where to put the money." The Toronto Stock Exchange's S&P/TSX composite index was down 64.57 points, or 0.51 percent, at 12,672.35. Financials, the index's most heavily weighted sector, dropped 0.6 percent. Royal Bank of Canada, the country's biggest lender, gave back 0.6 percent to C$63.97, and insurer Manulife Financial Corp fell 1.6 percent to C$17.38. Shares of energy companies shed 0.6 percent. Canadian Natural Resources Ltd fell 1.6 percent to C$31.01 and had the biggest negative influence on the market. The materials sector, which includes mining stocks, stumbled 0.5 percent. Teck Resources Ltd declined 1.6 percent to C$28.24. B2Gold Corp tumbled more than 8 percent to C$3.12. The gold producer said it is offering $225 million of convertible senior subordinated notes due 2018.