WASHINGTON—The Justice Department said Monday that it has charged hundreds of people in criminal and civil financial-fraud cases, as part of a stepped-up effort to stop scams targeting individual investors.

The Justice Department grouped the cases together under the name "Operation Broken Trust," but many of the cases were in progress before that operation started in August. In all, officials said that between Aug. 16 and Dec. 1 they have indicted 158 defendants and secured convictions of 104 individuals.

Monday's announcement comes as federal agencies and the Obama administration are facing pressure to punish big-name companies and individuals for their role in the financial crisis. So far, the U.S. has won few high-profile cases, compared with the aftermath of the savings-and-loan crisis and the dot-com bust.

"Some cases make big headlines; some perpetrators are high-profile. Many of the cases today do not share those characteristics," Securities and Exchange Commission Enforcement Chief Robert Khuzami said at a news conference at the Justice Department to announce the results of the probe.

The cases highlighted Monday mainly targeted what officials said were fraud figures and Ponzi-scheme operators around the country who victimized the elderly and other vulnerable people with pump-and-dump and other scams.