The FBI used "improper" methods to obtain personal information on Americans involved in terrorism investigations in 2006, the Department of Justice's inspector general reported Thursday, but corrective actions are underway and should be measurable next year.

Fulfilling the prediction laid about by FBI Director Robert Mueller last week, Inspector General Glenn Fine reported that National Security Letters (NSLs), also referred to as administrative subpoenas, were issued 49,425 times in 2006, up by nearly 5 percent over the previous year. A statistical sampling of those NSLs showed that 9.43 percent violated federal laws on getting and using the information.

"The report identified various intelligence violations by the FBI in NSL usage in 2006, such as issuance of NSLs without proper authorization, improper requests and unauthorized collection of telephone or Internet e-mail records due to FBI errors or mistakes made by the NSL recipients," reads an executive summary from Fine's office.

NSLs are issued by the FBI and other investigative organizations to entities such as banks and telephone companies, compelling them to provide certain information about a specific individual. They are issued in the course of criminal, financial, counter-terror or counter-intelligence investigations.

NSLs are to be kept secret by the person or organization to whom they have been issued, and someone revealing he or she is the recipient of an NSL can face prosecution.

A similar inspector general report last year covered calendar years 2003-2005, but the 2006 number of abuses was "significantly higher than the number of reported violations in prior years." The report noted that in 2006, FBI personnel self-reported 84 possible violations to headquarters. That compared to 48 violations found in Fine's initial audit.

The errors included issuing national security letters without proper authorization, improper requests and unauthorized collection of telephone or Internet e-mail records.

The report noted that the majority of violations were the fault of the FBI, but a fair number were also committed by the companies and individuals that responded to the letters. Fine said the problems were compounded because agents failed to recognize that the companies had turned over too much information and went ahead and used or loaded into bureau computers the inappropriately obtained information.

Since 2003, U.S. citizens and foreigners legally in this country have increasingly been the targets of the letters, rising from 39 percent of requests in 2003 to 60 percent in 2006, Fine reported.

FBI Director Robert Mueller told Congress last week that corrective actions have been implemented in the past year to make sure the FBI did not repeat the errors in issuing NSLs. Department officials say they believe the next report, covering 2007, will show marked improvement.

Among the 17 new recommendations offered by Fine to help the FBI's use and policing of the letters were added guidance and training for agents and regular monitoring of the handling of the letters.

Assistant FBI Director John Miller said new rules require that an attorney review the letters before they are sent, a new automated system was put in place to reduce errors and improve the accuracy of reports to Congress, and agents are getting more training about national security letters.

"We are committed to using them in ways that maximize their national security value while providing the highest level of privacy and protection of the civil liberties of those we are sworn to protect," Miller said.

Fine said the FBI and Justice Department had made significant progress in implementing revised procedures since last year but some measures still are not fully in use or tested. He reserved judgment on whether corrective actions under way will work.

"It is too early to tell whether these measures will eliminate fully the problems," he wrote in the 200-page report.

House Judiciary Committee Chairman John Conyers acknowledged that "the FBI has taken important steps to repair" the problems but said, "I remain disappointed."

Conyers, D-Mitch., said his committee would question FBI Director Robert Mueller about the inspector general's report at a hearing next month.

Conyers' Republican counterpart, Texas Rep. Lamar Smith, commended the FBI for its progress.

“I am pleased with the efforts of the FBI and the Department of Justice to ensure that Americans’ civil liberties are protected," Smith said. “Since last year’s report, the FBI has implemented additional levels of review ... These additional steps are helping the FBI protect the privacy of the American people without interfering with national security investigations."

Fine also commended the FBI for devoting "significant time, energy and resources to ensuring that its employees understand the seriousness of the FBI's shortcomings." He emphasized that "continual attention, vigilance and reinforcement by the FBI and the department" will be required.

But he did criticize one of the Justice Department's reform efforts — an August 2007 proposal by a working group under Justice's chief privacy officer to come up with a system to "label or tag NSL-derived information or to minimize the retention and dissemination of such information."

FOX News' Ian McCaleb and The Associated Press contributed to this report.