VIDEO: Secret Service Head Grilled on White House Breach

Facing blistering criticism from Congress, Secret Service Director Julia Pierson said Tuesday she takes full responsibility for the breach of White House security in which a man with a knife entered the mansion and ran through half the ground floor before being subdued, reports the Associated Press .

"It's unacceptable," Pierson told lawmakers, promising a review of how the storied but blemished agency carries out its mission of protecting the president and how it failed to intercept the intruder much earlier.

"I'll make sure that it does not happen again," she said.

Pierson also said there have been six fence-jumpers this year alone, including one just eight days before Army veteran Omar J. Gonzalez jumped the fence on Sept. 11.

Members of Congress briefed by the agency apparently weren’t told of the full extent of the breach. Details only emerged later.