WASHINGTON (Reuters) - The FBI possibly violated the law or its rules more than 1,000 times since 2002 in collecting data about phone calls, e-mails and financial records while investigating terrorism or espionage suspects, FBI officials said on Thursday.

The potential violations found by an FBI audit were far greater than the approximately two dozen previously documented violations in a U.S. Justice Department report released in March that was based on a much smaller sampling, they said.

The vast majority of newly discovered violations were instances in which companies, such as telephone and Internet providers, gave more information than the FBI sought, the officials said.

They said the FBI has drafted new guidelines in an effort to prevent future abuses, but civil liberties groups and Democrats in Congress expressed doubt that they would be sufficient to protect the privacy of Americans.

The ongoing audit concerned the use of national security letters, which allow the FBI to compel the release of private information such as communications or financial records without getting court approval.

Their use has grown dramatically, mainly as a result of powers granted to the FBI under the USA Patriot Act, an anti-terrorism law Congress approved after the September 11 attacks.

Caroline Fredrickson of the American Civil Liberties Union said the new guidelines were not enough. "Congress must go back to the legislative drawing board and rein in the broad ... authorities expanded by the Patriot Act," she said.

Rep. Edward Markey, a Democrat from Massachusetts, urged Congress to hold oversight hearings to determine whether changes in the law were required to prevent future violations.

Rep. Jerrold Nadler, a Democrat from New York and chairman of a House Judiciary subcommittee, said: "The new FBI guidelines ... fall far short of protecting the privacy of innocent Americans." 

Justice Department inspector general Glenn Fine in the March report sharply criticized the FBI for how it demanded and received records such as customer information from telephone companies, Internet service providers, banks and credit card firms.

The FBI audit sampled about 10 percent of the FBI's national security investigations since 2002 and the officials said they expected the full audit to be completed soon.

FBI officials said the audit found no evidence that any agent knowingly or willingly violated the laws or that supervisors encouraged such violations. The report in March also found no evidence of intentional criminal misconduct.