Corporate default rates could accelerate from next year as the recent turmoil in credit markets has erased the appetite for risky investments, ratings agency Standard & Poor's said in a report.

There is a material risk that defaults could be more severe beyond the one-year forecast horizon, S&P said in a report published on Tuesday night.

Global corporate speculative-grade bond default rates held at 1.02 percent in August. Default rates remain near record lows as hedge funds, private equity firms and other financial institutions have poured billions of pounds into refinancings and restructurings.

However, investors are now shying away from risky investments, the report said.

In the U.S., there were no high-yield issuances in August, compared with four in July and a monthly average of 38 during the first half of this year, S&P said.

Market volatility shut down the issuance pipeline in the U.S., the report said.

The agency maintained its 1.4 percent U.S. speculative-grade default forecast by the end of the year.

The leaks in the credit markets will continue to sap strength, even though defaults might be staved off in the next six months, partly because of structural concessions that avert payment default, S&P said.