By EILEEN SULLIVAN

Associated Press

WASHINGTON -- Three Secret Service officers have been put on administrative leave after the security breach at last week's White House dinner, an episode President Obama said hasn't shaken his confidence in his protectors.

The president nevertheless acknowledged Thursday that "the system didn't work the way it was supposed to."

Despite the screw-up, the president was never at risk, Secret Service Director Mark Sullivan told Congress on Thursday.

"Pure and simple, this was human error" in which normal security protocols were not followed, Sullivan testified. So far, the service's continuing investigation has found three people from the agency's uniformed officer division responsible for the security breach and all three have been taken off duty until a review of the matter is completed, he added.

Sullivan had said early on that it was the Secret Service's fault that a Virginia couple made its way to the administration's first state dinner without an invitation.

The couple -- Tareq and Michaele Salahi -- and White House social secretary Desiree Rogers were invited to testify Thursday, but all three declined.