U.S. Deputy Attorney General Paul McNulty resigned on Monday, amid investigations into the firings of eight federal prosecutors last year, the Justice Department said.

In a statement, Attorney General Alberto Gonzales said McNulty, who had become so far the highest ranking official to resign over the firings, would leave later this summer after more than eight years with the department.

The Justice Department "will be losing a dynamic and thoughtful leader with the departure of Deputy Attorney General Paul McNulty," Gonzales said.

McNulty, the No. 2 official at the Justice Department, first announced his resignation at a closed-door meeting in San Antonio, Texas, U.S. media reported.

Gonzales did not mention in his statement about the firings, which lawmakers said might be politically motivated and had led to the resignation of two senior Justice Department officials, including Kyle Sampson, Attorney General Alberto Gonzales' former chief of staff, White House liaison Monica Goodling.

McNulty was confirmed as deputy attorney general in March 2006,and before that, he served as acting deputy attorney general since November 2005.

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

Congress has been investigating the firings, and lawmakers of both parties have called Gonzales to resign.

At a congressional hearing in February, McNulty said at least one of the fired prosecutors was ordered to leave to make room for a protege of the president's chief political adviser Karl Rove. But Gonzales has maintained that the firings were proper, and refused to resign.

Gonzales has argued during hearings in Congress that while the process to fire the prosecutors last year was "flawed," but his decision to ask them to resign was "justified and should stand."

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