The director of the US Secret Service has resigned in the face of revelations of security breaches and an erosion of confidence over the safety of president Barack Obama and his family.

The US Secret Service director has told lawmakers she takes full responsibility for the serious breach of White House security when an Army veteran with a knife climbed the fence and made his way into the executive mansion before he was tackled.

An intruder who jumped a fence at the White House made it further inside the building than the US Secret Service has publicly acknowledged, according to reports.

Investigators found more than 800 rounds of ammunition in the car of the man accused of scaling the White House fence and sprinting inside the building, a US prosecutor said today. A machete and two hatchets also were found.