WASHINGTON — The Securities and Exchange Commission said Sunday it is immediately opening a probe to prevent the spread of false information used to manipulate securities prices.

SEC Chairman Christopher Cox said the investigation is aimed at "ensuring investors continue to get reliable, accurate information about public companies in the marketplace."

The probe comes amid a new bout of turmoil that has gripped investors. Questions have been swirling about the financial health of mortgage giants Fannie Mae and Freddie Mac as well as Lehman Brothers Holdings Inc.

Earlier this year, a run on Bear Stearns pushed the investment bank to the brink of bankruptcy and into a takeover by JPMorgan Chase. Bear officials blamed market rumors for the run.

The investigation will be conducted by the SEC's Office of Compliance Inspections and Examinations as well as the Financial Industry Regulatory Authority and New York Stock Exchange Regulation Inc.

Cox said the probe will provide an opportunity to make sure brokers and investment advisers have "appropriate training for their employees and sturdy controls in place to prevent intentionally false information from harming investors."

The probe is separate from SEC's investigations, already under way, into alleged intentional manipulation of securities prices through "rumor-mongering and abusive short selling," the agency said in a statement.