A report by Inspector General Glenn Fine's office sharply criticised the FBI for how, without a court order, it demanded and received records such as customer information from telephone companies, Internet service providers, banks and credit card firms.

"We believe the improper or illegal uses we found involve serious misuses of national security letter authorities," Fine said in releasing the report.

National security letters allow the FBI to compel the release of private information without getting authority from a judge or grand jury. The FBI can get the records but not the content of communications, Justice Department officials said.

Democrats in Congress vowed to investigate the findings in the report, which came as they stepped up criticism of President George W Bush's administration for weakening protections on civil liberties as part of its war on terrorism.

FBI Director Robert Mueller acknowledged at a news conference that the report found serious deficiencies.

"I am the person responsible, I am the person accountable and I am committed to ensuring that we correct these deficiencies and live up to these responsibilities," he said, noting the FBI is sworn to uphold privacy protections and civil liberties.

Attorney General Alberto Gonzales told a privacy rights group that he was upset when learnt the FBI did not have sufficient controls, did not provide adequate training and failed to follow its own policies.

MISTAKES MADE

"Although I believe the kinds of errors we saw here were due to questionable judgement or lack of attention, not intentional wrongdoing, I want to be very clear: there is no excuse for the mistakes that have been made and we are going to make things right as quickly as possible," Gonzales said.

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

In investigating abuses of authority, the report found 26 possible violations, including requesting information without adequate authorisation, improper requests under the law and unauthorised collection of telephone or e-mail records.

Of the 26 cases, 22 were the result of FBI errors and four were caused by mistakes by those who received the request for the information, the report said.

In reviewing 77 investigative files in FBI field offices, the report found that 17 of them, or 22 percent, contained one or more possible violations not identified by the field office or reported to FBI headquarters as required.