By Sam Forgione NEW YORK, Sept 11 (Reuters) - Investors pulled $6.8 billion out of U.S.-based bond mutual funds in the latest week, marking the sixth straight week of outflows from the funds as selling pressure on bonds continued, data from the Investment Company Institute showed on Wednesday. The outflows in the week ended Sept. 4 were down from investor withdrawals of $9.3 billion the prior week, according to data from ICI, a U.S. mutual fund trade organization. The outflows showed a persistent flight out of bonds. Data showing upwardly revised U.S. economic growth and strength in manufacturing bolstered expectations that the U.S. Federal Reserve will soon start reducing its $85 billion in monthly bond purchases. Investors have fled bonds on fears that a pullback in the Fed's stimulus will cause interest rates to spike higher, which would weaken bond prices. The Fed's bond-buying has been a major source of support for both stock and bond markets this year. Investors pulled $2.05 billion out of municipal bond funds in the latest week, down from outflows of $2.9 billion the prior week but still marking the 15th straight week of outflows. Stock funds, meanwhile, attracted $904 million in new cash over the weekly period. Inflows of $1.6 billion into funds that hold non-U.S. stocks, a modest increase from the prior week, accounted for the total inflows. Funds that hold U.S. stocks had outflows, meanwhile, of $694 million, marking the fourth straight week of outflows. The outflows came despite a 1.1 percent rise in the benchmark S&P 500 stock index on the strong U.S. economic data. Hybrid funds, which can invest in stocks and fixed income securities, had inflows of just $263 million, marking the smallest inflows into the funds in 10 weeks. The following table shows estimated ICI flows for the past five weeks (all figures in millions of dollars): 8/7/13 8/14/13 8/21/2013 8/28/2013 9/4/2013 Total Equity 3,609 1,512 1,338 -212 904 Domestic 552 -766 -384 -1,351 -694 World 3,057 2,278 1,722 1,138 1,597 Hybrid* 1,328 1,588 1,106 1,148 263 Total Bond -2,084 -3,881 -11,142 -9,303 -6,766 Taxable 43 -1,793 -7,374 -6,390 -4,718 Municipal -2,127 -2,088 -3,769 -2,913 -2,048 Total 2,853 -782 -8,698 -8,367 -5,599 *Hybrid funds can invest in stocks and/or fixed income securities.