The Justice Department's internal watchdog said Monday it has opened an investigation into the agency's use of information gathered in the government's warrantless surveillance program.

In a letter to House Judiciary Committee leaders and obtained by The Associated Press, Inspector General Glenn A. Fine said his investigators would focus on the Justice Department's role in carrying out the spying program run by the National Security Agency.

Fine wrote that he wants to ensure that prosecutors are following laws governing the handling of information NSA gathers when spying on suspected terrorists in the United States.

"After conducting initial inquiries into the program, we have decided to open a program review that will examine the department's controls and use of information related to the program," Fine wrote in the four-paragraph letter.

The review comes a week after a federal judge ruled that the NSA is not required to publicly release details about its secret wiretapping program, in which the agency monitors phone calls and e-mails between people in the U.S. and people in other countries when a link to terrorism is suspected.

Civil liberties groups criticize it as an expansion of presidential power, but the Justice Department says it is a necessary tool to fight terrorism.

"This is a long overdue investigation of a highly controversial program," incoming House Judiciary Chairman John Conyers, D-Mich., said in a statement.

The White House agreed to give investigators special clearances to probe the program, Fine noted in his letter to Conyers and the panel's current chair, Rep. James Sensenbrenner, R-Wis. The request for clearances came Oct. 20, and was approved last week -- following the Nov. 7 elections that gave Democrats control of Congress.

Earlier this year, Fine's office said it did not have jurisdiction to open an investigation into the legality of the administration's domestic eavesdropping program. At the time, Fine's office referred calls for an inquiry to the Justice Department's Office of Professional Responsibility, which reviews allegations of misconduct involving employees' actions when providing legal advice.

The Office of Professional Responsibility was denied extra security clearances to conduct an investigation that would include looking at some classified documents and other information that the Justice Department already possesses.