The US Secret Service is an "insular" agency that needs a new director hired from outside to improve training, according to former government officials who examined the embattled agency after a man with a knife stormed the White House.

An executive summary of the highly classified review revealed deep problems at the top of the Secret Service, which is charged with guarding the US president and other senior government officials.

"The next director will have to make difficult choices, identifying clear priorities for the organisation and holding management accountable for any failure to achieve those priorities," the group wrote after interviewing 50 Secret Service employees.

"Only a director from outside the Secret Service, removed from organisational traditions and personal relationships, will be able to do the honest top-to-bottom reassessment this will require.''

Homeland Security Secretary Jeh Johnson said in a statement that the recommendations are "astute, thorough and fair".

Johnson appointed a four-member independent panel in October after a September 19 intrusion by an Iraq war veteran who scaled the White House fence, sprinted across the lawn and got deep inside the mansion before an off-duty agent stopped him.

Julia Pierson resigned under fierce criticism on October 1, less than two weeks after the September 19 intrusion. That fence jumper breach came a day after the disclosure that an armed private security contractor rode on an elevator with Obama in Atlanta in a breach of protocol earlier in September.

The incident prompted the panel's first recommendation to build a better fence "as soon as possible". It recommended one that is at least 120 or 150 cm higher and curves outward at the top to give agents more time to assess the risk of a jumper.

In November, an internal review concluded that training, poor staffing and a series of missteps contributed to the breach.

Republican Representative Jason Chaffetz, incoming chairman of the Oversight and Government Reform Committee, on Thursday promised an independent congressional review of the agency.

Source: Agencies