U.S. Attorney General Alberto Gonzales's top aide Monica M. Goodling abruptly resigned on Friday, days after she refused demands to testify before Congress about her role in the firings of eight federal prosecutors last year.

Goodling, who was also the department's White House liaison, gave no reason in a three-sentence resignation letter to Gonzales, less than two weeks before Gonzales' planned testimony before Congress over the firings.

Eight federal prosecutors were fired by the Justice Department last year, which lawmakers said might be politically motivated.

Members of Congress, who have been investigating the firings and have called Gonzales to resign, have asked some White House and Justice Department officials to testify in their investigation.

Goodling, who had taken a leave amid an uproar in Congress overthe dismissals, had refused to testify by asserting her Fifth Amendment right against self-incrimination.

Kyle Sampson, Gonzales's chief of staff, resigned last month amid revelations that White House staff initiated the decision to fire federal prosecutors.

There are more than 90 federal prosecutors in the United States, who are appointed to four-year terms by the president.