WASHINGTON -- FBI Director Robert Mueller has apologized to the editors of The New York Times and The Washington Post for improperly obtaining phone records of the newspapers' reporters while investigating terrorism four years ago.

Mueller called Post Executive Editor Leonard Downie Jr. and Times Executive Editor Bill Keller on Friday to express regret that agents did not follow proper procedures in 2004 when they obtained the phone records of a Post reporter, a Post researcher and two Times reporters. All four were working in Indonesia and writing about Islamic terrorism at the time.

Mueller and other FBI officials told the newspapers that agents obtained the records under a process that allowed them to bypass a grand jury review in emergency cases. The incident came to light through a review by the Justice Department's inspector general of bureau procedures that enabled the FBI to obtain thousands of records from phone companies after the Sept. 11 attacks.

In the case of the newspaper reporters, agents obtained toll phone records — records of incoming and outgoing calls, but not details of conversations — using what are known as "exigent circumstances" letters.

Last year, the inspector general uncovered 700 cases in which FBI agents obtained telephone records through "exigent letters," which asserted that grand jury subpoenas had been requested for the data when in fact such subpoenas never had been sought. The FBI eliminated use of the letters in 2007.

Both Keller and Downie said they are seeking more information on the incidents, and Keller said he also wants to know how the FBI intends to prevent future incidents.

Deputy Assistant FBI Director Mike Kortan said in a statement that no investigative use was made of the reporters' phone records, and that "safeguards are now in place that we believe would prevent this from recurring."

Because of possible First Amendment violations, requests for reporters' phone records are supposed to receive an even higher level of scrutiny before they can be approved — usually requiring the approval of the attorney general or another high-ranking Justice Department official.