The U.S. Securities and Exchange Commission filed civil fraud charges Friday against six former executives of government-backed mortgage giants Fannie Mae and Freddie Mac, accusing them of deceiving investors about the firms' involvement with risky subprime loans.

Accused are the former CEOs of Fannie and Freddie, Daniel Mudd and Richard Syron, respectively, along with four other erstwhile senior executives of the two companies.

The defendants knowingly approved statements that misrepresented the extent to which the firms underwrote subprime mortgages in the years leading up to the 2008 financial crisis, the SEC said.

Fannie Mae, which dates from 1938, and Freddie Mac, founded in 1970, were created to promote liquidity in the mortgage market.

Known as government sponsored enterprises, or GSEs, Fannie and Freddie eventually went from being autonomous federal agencies run by civil servants on fixed salaries to public companies with CEOs who stood to make seven-figure incomes.

The 2008 financial meltdown prompted the government to place the two companies into conservatorship overseen by the Federal Housing Finance Agency.

Both Fannie and Freddie have signed agreements accepting the SEC's declaration of facts and pledging to cooperate with the agency's investigation of the former executives.

"Fannie Mae and Freddie Mac executives told the world that their subprime exposure was substantially smaller than it really was," Robert Khuzami, director of the SEC's Enforcement Division, said in a statement.

"These material misstatements occurred during a time of acute investor interest in financial institutions' exposure to subprime loans, and misled the market about the amount of risk on the company's books," Khuzami said.